What can I do to protect myself from computer viruses and Trojans?

These days, practically everyone's online, downloading and exchanging files, and developers are in such a hurry to get their Web sites up or their files out that checking for a nasty bug is more of a courtesy than a requirement. If you're not careful, your computer can end up with a nasty virus that makes your files act oddly, crashes your computer, pops up bizarre messages, or worst ofall, destroys your operating system.A computer virus is the most subtle of computer problems. It usually loads itself into your computer system when you run a program to which it has attached itself. From the computer system, it'll then reproduce itself, much like a biological virus would, by attaching copies of itself to other programs on your hard drive. What it does then depends on the malevolence of its creator. Some viruses are nothing more than a practical joke. They may bring up a message like "Merry Xmas" or melt your display. Most of them though, either start destroying your system or your files immediately or on a date specified by their creators—like the much-publicized Michelangelo virus, which erases important pieces of your system on March 6. "Trojan horse" programs are similar to viruses in their effect on your system, but they can't reproduce themselves. They're usually a program disguised as something you might want to download onto your computer—for instance, a rogue, modified version of PKWare's PKZIP utility. But when you run the new program you just found, it can do anything from popping up a message to erasing your hard disk, as the roguePKZIP utility really did.In either case, you have to actually launch the infected program or the trojan horse for it to infiltrate your system. Though hoax e-mails, like the one about the "Good Times" virus try to make you believe otherwise, neither a virus nor a trojan horse program can do anything if you simply leave the malevolent file sitting on your hard drive.Finding out that you copied a trojan horse onto your computer is remarkably easy. You launch the program, and the next thing you know, something completely unexpected happens—maybe your system is gone or your computer is laughing maniacally at you. But unless you notice your computer acting oddly before the virus has done its worst damage, you may very well not know you have it until it's too late.Protect YourselfThere are a few basic rules that computer users should follow to short-circuit viruses. The best known bit of advice is this: Never open any attachment unless you know who it's from and why they are sending it. Refusing to open unsolicited e-mail of any kind is the only sure-fire way to sidestep all forms of trouble.Anti-virus software is crucial to preventing virusattacks, but this strategy only works if users update their software.Unfortunately, 'keeping it current' means updating it weekly, at least but most products today allow one to automate this process, but file downloads can be large and slow.Factors to consider when buying an anti-virus package include cost, quality of tech support, how frequently the package self-updates and the platforms supported by the program.Common sense is another good weapon in the fight against viruses. Be wary of opening any email attachments, even from your firends , especially if it has been forwarded to them.Set up your anti-virus product so that it automatically scans incoming e-mail and avoiding e-mail software that allows automatic launching of attachments.If all of this sounds like a lot of work, it is. There is always a tradeoff between ease of use and security but the extra time you spend updating your anti-virus software now will save you hours of time and buckets of frustration later.If you don't keep it updated, you might waswell be completely unprotected.