14 sneakiest viruses

As is the case with any real-world fortress, most computer operating systems have security holes and flaws somewhere - it's just a matter of whether the computer company or computer hackers discover them first. Such is the case with a recent security hole discovered on computers running Windows XP, Windows 2000, and Windows Server 2003. The hole essentially leaves computers totally open to hackers, with no involvement from computer users at all! Luckily, Microsoft last week discovered this flaw and took the rare step of immediately releasing a security patch before any evildoers could wreak havoc. If you haven't updated your Windows machine with the latest security patches, then do so immediately. You should have already been updated if your computer is set to Automatic Updates in the Control Panel (click on Start, then Control Panel, then Automatic Updates). You can also download the patch yourself by going to the Microsoft Download Center.

This virus is one of the nastiest and most prolific out there. It's a backdoor Trojan - malicious software disguised as a harmless program - that is spread to PCs via fake news and holiday greeting card e-mails. Once infected, your computer becomes part of a botnet, a network of computers running and spreading the malware at an alarmingly fast rate -- so essentially your computer not only slows down, but also serves as a perpetrator of the crime. How to protect yourself? Don't open any files in e-mails from people you don't know, turn on your e-mail program's spam prevention tool, and make sure your virus protection software is up-to-date.

Mal/Hupig-D runs in the background of Windows and steals your passwords, credit card information, and the like. Virus scanners look for it now, but rely on your common sense first and don't click on that e-mail. If you'rew worried that your computer might be infected with it, don't enter your passwords or credit card information until you get it looked at by a computer professional.

I know you may love those funny videos your friends send to you on Facebook, but you may have to forget clicking on any links from friends in the near future. That's because a Trojan horse that purports to be a legitimate e-mail from a Facebook friend actually contains W32.Koobface worm, which looks for a cookie on your computer that enables it to take over your Facebook account and send itself to all your friends! Here's what to watch out for: E-mails that have flattering subject lines about who a hot crush someone has on you, or how great you look in some video.

The e-mail itself will have a link to a YouTube like link that leads you to a fake YouTube page. On that page, you're asked to download a video player upgrade. Whatever you do, don't download and install that upgrade, or your machine will be infected. But before you even get to that point, you might just double-check with your friends who like to send videos to make sure what they've sent is legit. It may take the fun out of video sharing, but better safe than sorry!

Sorry, Mac users, but you're in danger too. This Trojan affects computers using Mac OS X 10.4 or 10.5, and lets the bad guys use your Apple Remote Desktop agent for a host of disturbing activities. The virus can be used to monitor your keystrokes, transmit passwords, turn on file sharing, take screenshots, and, creepiest of all, take pictures with the built-in iSight camera -- all unbeknownst to you! It's spread through downloads that you have to agree to, so if you stay sharp, avoid sketchy utilities, and keep your anti-virus protection current, you'll be fine.

Facebook users have probably seen it happen - a friend posts a link to a Web site on other people's walls, urging them to see a funny video or find out who has a crush on them. Just as with spam e-mails, the link takes you to a bogus site that tells you to download a newer version of Flash, which turns out to be Troj/Dloadr-BPL. This virus then lets hackers take over your computer to spread spam and malware. Basically, criminals are using Facebook because they think users are more likely to visit a link if a friend tells them to. The solution? Don't click it, or better yet, stop using those annoying Facebook Wall programs anyway. Be particularly wary of videos posted by people who don't usually send videos (at least to you).

Beginning in 2005, the Zlob Trojan has been infecting computers by convincing users they need to download a codec to view a spam or porn video. The Trojan then reroutes your internet traffic through a hacker's server. The end result is a computer that shuts down randomly and reboots with confusing text messages. The newest variation of Zlob actually works on your Wi-Fi router by running through a list of default username and password combos, which many users never bother to change. In addition to the usual anti-virus and trusted downloading advice, this time make sure to change your router's security settings and passwords on a regular basis. It's that easy.

Starting around the last new year, the Mebroot virus began infiltrating computers' master boot records, the part of the hard drive that loads the operating system, by installing itself from untrusted Web sites. The virus installs keyloggers that are triggered when the infected computer is used to visit any of 900 financial sites, stealing usernames and passwords any time they're typed (and thus eventually stealing your money or identity). Unfortunately, his rootkit hides from most virus protection software, but you can visit GMER to get software that scans and deletes this menace.

A new threat that's popped up recently uses flash banner ads to take over your computer's clipboard through the Mozilla Firefox Web browser. You'll know your computer, either Mac or PC, is infected once your clipboard will only paste a link to a site that sells a bogus security program. Many people are led to the sites with the infected ads through spam e-mails purporting to come from CNN or MSNBC. It seems you can get rid of the infection by restarting your computer or killing the Firefox process, and downloading FlashBlockers for the browser can only help.

This crafty file is mainly getting into computers via the UPS e-mail scam. The Trojan comes in an attachment that pretends to be an invoice for an undeliverable package, and then stealthily allows your financial data to be stolen by foreign crooks. UPS rarely sends attachments, so if you receive something suspicious, don't open it and contact customerservice@ups.com.

Recently, an iPhone-specific Trojan has been spreading via e-mails that offer a free game for the Apple product. The virus hides in a file named "Penguin.Panic.zip," which is attached to e-mails with subject lines like "Virtual iPhone games!" and "Apple: The most popular game!" The Trojan actually infects Windows machines, allowing hackers to take control over it. So, to protect yourself, don't download any free games like this!

This Trojan is unique in that when it infects your computer, it encrypts your files and demands payment, usually around $100, to unlock them. Experts are still unsure how this malware is spread and how to protect against it outside of constantly backing up your files. On the bright side, the author of the code was recently identified as a Russian citizen, but authorities have yet to do anything about it.

Looking for a deal on your anti-virus software? If you're not careful, you could end up downloading a virus that'll scam you out of your hard-earned money. While there are a variety of these threats around the Web, a current prevalent one -- the FakeAV-AD Trojan -- pretends to be a free copy of Norton AntiVirus 2008. If you download it, you'll get a number of security alerts that tell you to buy the full version with your credit card. Guess what happens next? The sneakiest part about this site, though, is that it comes up as a Sponsored Link in Google if you're searching for free virus protection.

Last month, a family of malware called Rogue Security applications comprised over 60% of computer threats. Much like the fake Norton link, the variations of this Trojan convince users to download security programs that intend to control your computer and rip you off. Most often, they're downloaded from those popup ads that say your computer is infected, leading you to download the file even if you try to close the window. There are many versions of this Trojan, some of which resist anti-virus programs, so be very careful, but for starters, make sure your browser's pop-up blocker is enabled.