Much of the world's transactions, whether it is business or personal, are now done online. From social interaction to keeping track of finances, the Internet is now a very large part of the average citizen's life. The Internet is not without its own set of risks, however. Should you encounter a virus, your private information could become compromised, data destroyed and hardware completely fried. Not all viruses are created equal, however. Some viruses have produced billions of dollars in damages. Here is a look at 10 of the most expensive computer viruses of all time, and how to avoid a similar devastation in the future.

MyDoom
The most devastating computer virus to date is MyDoom, which caused over $38 billion in damages. In addition to being the most expensive virus to date, its effects were far-reaching and fast-moving. When a user was infected with the virus it creates network openings which allowed others to have access to your computer. In addition, the virus also had the ability to open random programs. In 2004, an estimated 25% of all emails had been infected by the virus.

SoBig
Another harmful and expensive computer virus is SoBig. In 2003, the SoBig virus caused over $37.1 billion in devastation. This fast-spreading virus circulated through email as viral spam, and if exposed, the virus had the capability to copy files, emailing itself to others and causing serious damage to computer software and hardware.

ILOVEYOU
ILOVEYOU is another particularly malicious virus that spread quickly through email, websites and file sharing. The ILOVEYOU virus, or the "Love Letter" worm, affected more than 500,000 systems in 2000 and produced over $15 billion in damages, including $5.5 billion in the first week alone. The virus replicated itself and exposed itself to everyone in the owner's contact list. This virus was a pioneer for other viruses, as it was one of the first to attach to an email.

Conficker
The Conficker virus caused over $9.1 billion in damages in 2007 and infected millions of computers around the world. The virus scanned computers for weaknesses and vulnerabilities, logged keystrokes and downloaded code from hacker-selected websites and more.

Code Red
One of the most well-known viruses to date is the Code Red virus. It caused over $2 billion in damages in 2001, and had the ability to break into computer networks and exploit weaknesses in Microsoft software. Once the virus infected the machine, it actively looked for other machines on the networks to attack.

Melissa
The Melissa virus was a particularly slimy virus that sent out infected Microsoft Word documents through Microsoft Outlook, delivering viral messages to everyone listed in the Outlook address book. The messages appeared to be coming from the Outlook owner, but was really the Melissa virus at work. A tell-tale indicator that Melissa had infiltrated your Outlook is if your contacts had received an email from you with the message: "Here is that document you asked for … don't show anyone else." There would be a word document attached, complete with the Melissa virus. In 1999, Melissa caused $1.2 billion in damages.

SirCam
SirCam was a worm that caused over $1 billion in damages in 2001. This virus had the ability to compromise confidential information, delete items or use up space on your hard drive until there was not enough memory to store anything else.

SQL Slammer
SQL Slammer is a virus that greatly affected banks and caused Internet speed to lag significantly across the globe. SQL Slammer caused an estimated $750 million in damages in 2003, and affected 200,000 computers worldwide.

Nimda
Nimda is one of the Internet's most widespread viruses and among the costliest as well. The virus caused $635 million worth of damages in 2001 and caused Internet browsing time to slow significantly. Additionally, it could affect a user's email account and send out a read-me file to all contacts listed in the email address book. The virus caused traffic and Internet speeds to slowdown.

Sasser
Sasser created quite a bit of trouble in 2004 when it piled up $500 million in damages, devastated the British Coast Guard mapping system and caused numerous canceled flights. The creator of Sasser was identified as a teenager from Germany, and was quickly apprehended when one of his "friends" turned him in for a $250,000 bounty posted by Microsoft.

The Bottom Line
While the Internet can be a wonderful resource for doing everything from communicating with friends and colleagues to checking your bank statement, it is not necessarily the safest of places to perform such transactions when viruses are lurking in the midst. Protect yourself and your computer with quality anti-virus software, and continue to browse safely on the Internet.

Machines running the decade-old Windows XP make up a huge reservoir of infected PCs that can spread malware to other systems, a Czech antivirus company says.

Windows XP computers are infected with rootkits out of proportion to the operating system's market share, according to data released last week by Avast Software, which surveyed more than 600,000 Windows PCs.

While XP now accounts for about 58 percent of all Windows systems in use, 74 percent of the rootkit infections found by Avast were on XP machines.

XP's share of the infection pie was much larger than Windows 7's, which accounted for only 12 percent of the malware-plagued machines -- even though the 2009 OS now powers 31 percent of all Windows PCs.

Rootkits have become an important part of the most sophisticated malware packages, particularly botnets, because they mask the infection from the user, the operating system and most security software. By installing a rootkit, the hacker insures the compromise goes undetected as long as possible, and that the PC remains available to the botnet's controller for nefarious chores, such as sending spam or spreading malware to other machines.

Avast attributed the infection disparity between XP and Windows 7 to a pair of factors: The widespread use of pirated copies of the former and the latter's better security.

"According to our stats, as many as a third of XP users are running SP2 [Service Pack 2] or earlier," said Ondrej Vlcek, the chief technology officer of AVAST, in an interview Thursday. "Millions of people are out of support and their machines are unpatched."

Vlcek assumed that many of the people running XP SP2, which Microsoft stopped supporting with security patches a year ago, have declined to update to the still-supported SP3 because they are running counterfeits.

Although Microsoft serves everyone, even pirates, its monthly security patches and service packs, most security experts believe that users of illegal copies are very hesitant to upgrade or even patch for fear that they'll trigger the black screen and anti-piracy nag notices that Microsoft slaps on screens when it deems a PC is running a counterfeit copy of Windows.

Windows XP accounts for a disproportionate share of rootkit infections, but Windows 7 is under-represented. (Data: Avast, Net Applications.)

Vlcek urged users running legal copies to upgrade to XP SP3. "Moving to SP3 is the most basic thing that should be done," he said.

Also in play, said Vlcek, is Windows 7's stronger security, especially the 64-bit version.
"The 64-bit version [of Windows 7] has some technologies that really make it much more difficult for rootkits to infect the computer," said Vlcek, calling out that version's kernel driver-signing feature as key to keeping rootkits off machines.

But that hasn't completely protected Windows 7 64-bit, as Vlcek acknowledged.

"The surprising part to me was that I thought the Windows 7 [number] would be even smaller," Vlcek said.

Rootkits able to infect 64-bit copies of Windows 7 remain relatively rare, but they're certainly not unknown: The first popped up in August 2010, and a massive botnet some have called "practically indestructible" last month used a variant of the same malware to install a 64-bit rootkit on Windows 7.

That malware, which goes by a number of names -- Alureon, TDL, Tidserv and most recently, TDL-4 -- is especially devious, as it installs the rootkit into the Master Boot Record (MBR). The MBR is the first sector -- sector 0 -- of the hard drive, where code is stored to bootstrap the operating system after the computer's BIOS does its start-up checks.

By subverting the MBR, the rootkit is even tougher to detect, since it's already in place by the time the OS and security software are loaded into memory.

Avast found that rootkits which infected the MBR were responsible for 62% all rootkit infections.

Users who suspect that their PC is infected with an MBR-based rootkit can scrub their machine with one of several free rootkit detectors, including Avast's "aswMBR" and Sophos' "Anti-Rootkit."

     Computer viruses may seem to be only a nuisance to the casual computer user. If you see the bigger picture, though, just imagine how governments, schools, and businesses were affected when certain viruses attacked and crippled their systems.

     These viruses spread even faster than a cold virus, thanks to the global network of computers known as the Internet. With computers disabled, imagine the organizations depending on those machines to operate and provide services. This virus attack would result in millions, even billions of dollars in damages and losses. Though not all of these malicious computer programs are massively destructive, there are still some that have caused a lot of damage. Here are the top ten most destructive computer viruses of all time.

1. ILOVEYOU a.k.a. Lovebug/Loveletter Virus

     The ILOVEYOU virus was a computer virus that many consider to be the most damaging virus ever written. It spread itself by email in 2000 through an attachment in the message. Once opened, it loaded itself to the memory, infecting executable files. When a user received and opened the email containing the attachment “LOVE-LETTER-FOR-YOU.txt.vbs”, the computer became automatically infected. It then spread itself by infecting executable files, image files, as well as audio files like MP3s. After that, the virus sent itself to others by looking up the addresses contained in the MS Outlook contact list. The virus was written by a Filipino programmer who was still a college student at that time. He said the release of the virus was only “accidental.” This virus spread throughout the world in just a day, infecting computers of large corporations and governments, including the Pentagon in the United States. It caused billions of dollars in damages. The actual “damage” occurred during the removal of the infection from computers, as email servers and computer networks had to be shut down before the virus could be removed.

2. CIH a.k.a. Chernobyl Virus

     This virus was considered one of the most dangerous and most destructive viruses ever because it had the ability to remain undetected in a computer’s memory, infecting every application that was run. First released in 1998, the CIH virus infected executable files of the operating systems Windows 95, 98, and ME. This virus also was accidentally distributed by a software vendor, contributing to the massive infection of computers. What made this virus dangerous was that it had a trigger date. Once that date was reached, it overwrote the files on the hard drive and completely destroyed its contents. It also had the ability to overwrite the BIOS of the computer to prevent it from booting up. This virus was also known as the Chernobyl virus because some variants were set to destroy data in computers that coincided with the nuclear power plant accident.

3. Melissa Virus

     Released in 1999, the Melissa virus was another mass-mailing malware that was said to have infected up to 20 percent of computers worldwide. This included the networks of Microsoft, Intel, and other companies that relied on MS Outlook as their email client. Email servers around the world were forced to shut down in order to prevent the virus from spreading, as well as to remove the virus from their system. The virus came through email including an MS Word attachment. When opened, it emailed itself to the first 50 people in the MS Outlook contact list. It also overwrote the document files in the infected computer with quotes from the famous cartoon TV series “The Simpsons.”

4. Code Red

     The world had not yet recovered from the damage caused by the ILOVEYOU virus when Code Red was released in mid-2001. Unlike other viruses, this one only targeted certain computers running the Microsoft IIS (Internet Information Server) Web Server, exploiting a bug in the software. Once a computer was compromised by the virus, it would modify the handled website, displaying the message “Welcome to http://www.worm.com! Hacked by Chinese!” Then, it would later seek other computers running the web server software and do the same thing. After about two weeks of infection, the virus was programmed to launch DDoS (Distributed Denial of Service) attacks on certain websites, including the server of the White House.

5. Bagle

     Bagle was another classic type of mass-mailing malware, but was quite complex. First detected in 2004, it infected users through an email attachment, and also used email to spread itself. Unlike previous mass-mailing viruses, Bagle did not rely on the MS Outlook contact list to make a list of where to send itself. It harvested email addresses from various document files stored in the infected computer – from plain-text files to MS Excel files. The danger of this virus was that its design opened a backdoor where a remote user – probably the author or a group of hackers - could gain access and control of the infected computer. It could download additional components to either spy and steal information from the user or launch DDoS attacks to certain networks and computers. Though the original Bagle virus was designed to stop spreading after January 2004, hundreds of variants today are still out there, spreading.

6. Blaster

     The Blaster virus was a complex malware that spread itself not through email, but through a vulnerability in both the Windows 2000 and Windows XP machines. This malicious software was detected in mid-2003 and by then had infected hundreds of thousands of computers. Once a computer was infected, it displayed a message box indicating that the system would shut down in a couple of minutes. It was also programmed to launch a DDoS attack to a server run by Microsoft by April 2003, but was already contained by that time. Discovered in the code was a hidden message to Microsoft founder Bill Gates saying “Billy Gates, why do you make this possible? Stop making money, and fix your software!”

7. Sasser

     Sasser was another complex computer virus that crippled thousands of computers, and was written by a 17-year-old German student in 2004. Sasser did not spread through email, and did not require any human intervention to compromise computers. It infected computers by exploiting vulnerability present in both Windows 2000 and Windows XP machines, known as the RPC (Remote Procedure Call) exploit - the same vulnerability used by the Blaster virus. Sasser successfully infected and shut down thousands of computer networks in just a matter of days. After infecting a computer, it is programmed to access the Internet to search for other vulnerable machines so that it can infect them. Sasser also displayed a notice indicating that the system was shutting down.

8. MyDoom

      Another mass-mailing virus that caused a lot of damage was MyDoom. Though it was primarily written to spread through email, it also successfully infected computers by infecting programs stored in the shared folder of the Peer-to-Peer software KaZaA. Detected in 2004, MyDoom slowed down global Internet access by ten percent, and caused some website access to be reduced by 50 percent. Upon infection, it looked for email addresses from contact lists and sent itself to any addresses it found. It was said that during the first few days, one out of ten email messages sent contained the virus. It was only stopped from spreading after about a month. (For tips on eradicating mass mailing viruses, read Email Scanners - Protection from viruses and malware)

9. Sobig.F

     Computer users were still recovering from the damage caused by Blaster in 2003 when another mass-mailer known as Sobig.F attacked. This computer virus caused billions of dollars in damage by stalling or completely crashing Internet gateways and email servers, resulting in the merciless slowing down of global Internet access. It harvested email addresses from various documents found in the infected computers. The virus then sent itself to these addresses. It was able to send over a million copies of itself within just a few hours of the outbreak. By September of 2003, it had deactivated itself, having been programmed to do so. It then ceased to be a threat.

10. SQL Slammer

     SQL Slammer is the least damaging virus in this list. It still caused a considerable amount of damage, though, by overwhelming routers, causing them to shut down. The target of this virus was web servers running a vulnerable version of Microsoft SQL Server. Only computers that ran this server software were infected, but it caused the slowdown of Internet access around the world. In just under ten minutes, it was able to infect thousands of servers center away. Upon infection of a server, the virus generated random IP addresses through which it attempted to further infect other computers.

Conclusion

     The main reason why these computer viruses caused so much damage world-wide was because most people were not aware of such threats and were not protected against them. Today, there are still thousands of computers that remain infected or are continuously being infected by old and new viruses. To avoid this, it is very important to keep a good anti-virus software program running and frequently updated. Other safety precautions include having firewall software (Learn how to set up a firewall), and updating the programs that you use to access the Internet, including email clients, server software, and Internet browsers.

     Now that you know the worst that viruses and their ilk can do to your computer, it’s high time that you learn how to get rid of computer viruses, computer adware and Email SPAM.

     Nowadays, USB devices or flash disks are the modern diskettes. They are handier and can accommodate large amount of files because of its large storage capacity ranging from 128MB to 32GB. But did you know that these devices are also the best medium for viruses? Viruses from your USB can infect your computer silently because of its stealth features. This means that they can enter your system without your permission. There are different kinds of viruses that can harm your computer and that can also cause your system to run abnormally.

     There are certain viruses that will disable your tasks manager, shut downs your computer, make your computer slow down and more but the most common USB virus is the one who hides your files stored in your USB. You may think that your files had been deleted but normally, the virus will only hide it and you can still access your files by doing these steps: First, you need to go to your folder options. Second, go to the view tab and then select “Show hidden files, folders and drives” and press ok. Third check your USB if your file has been recovered. And lastly, highlight your hidden files and then uncheck the hidden option located in its properties.   

     To protect your computer from viruses, make sure that you have a reliable antivirus program to block viruses from entering your system, and also make sure that it’s up to date because there are new viruses out there that may not be detected by your antivirus if it’s not updated. And also, be careful in inserting your flash disks in internet café’s or shops because most of them do contain viruses.

     You may be using an antivirus program installed in your system but it may not be enough. In this case, you can use a program called USB DISK SECURITY to protect your computer. It will automatically detect if your USB has a virus and it will ask you to delete it. This will be your guard against USB viruses. This protection is real time and it will be scanning all your USB devices. I recommend this program to avoid further damage to your system caused by a virus. This can be the solution to your infected USB devices. For added security, you can also use antivirus programs that are installed directly to your USB to prevent viruses from entering your USB’s. This can help you prevent viruses.