"My computer is acting up. It must be a virus." You've undoubtedly heard comments like this or even thought this yourself. In actuality, most computer glitches are caused by software conflicts or user error.

Viruses aren't as common as other computer problems. They're found in about 0.15 percent of e-mails, according to the latest figures from MessageLabs, a provider of Internet security products that each day analyzes more than 180 million e-mails worldwide for its business clients.

That makes viruses less prevalent than phishing attacks that try to trick you into revealing your credit card, banking, or other personal information, which make up about 0.45 percent of e-mails. The most common e-mail problem, however, is spam, those unsolicited, untargeted commercial messages sent in bulk, with such messages comprising a whopping 44.96 percent of all e-mails.

But viruses do get a lot of attention, and it's easy to see why. They have an ominous and mysterious aura. And they can do serious damage, including wiping out all the data on your hard drive. Some may not do overt harm but instead scare you with a pop-up text message such as "Gotcha," a photo of a raised middle finger, or a sinister audio or video file.

Computer viruses are simply small computer programs. Like human viruses, computer viruses can replicate, spreading like a disease from one computer to another through e-mail or, less commonly, through infected CD-ROM discs, USB drives, music and other file-sharing networks, and Web sites.

All indications are that viruses are typically written by pranksters in their teens and twenties, according to virus experts. Some are written by truly disturbed individuals, the kind of sociopaths who indiscriminately slash tires. Some may be written in a more formalized way, by members of organized crime families or foreign terrorist groups. And some are intended as "good viruses" to delete other viruses but may inadvertently cause harm, for instance, by deleting a vital system file by mistake.

Viruses may be written from scratch by programmers. Or they may be created with virus-writing kits, requiring no programming knowledge. Some virus writers write viruses for the intellectual challenge, never intending to release them. Some of these viruses get released accidentally. Web sites and online chat rooms exist where virus writers ask questions, trade tricks, and boast of their exploits.

The first line of defense against viruses, as with every potential computer disaster, is to make regular backups of the vital data stored on your hard drive. Ideally you should periodically do this to a medium that's not continuously connected and accessible, to prevent a virus from infecting it too.

The next safety step is to use antivirus software. Top programs include Symantec's Norton AntiVirus, available separately or as part of other Symantec products, and McAfee VirusScan, also available separately or as part of a larger suite of other products.

Antivirus programs scan relevant files looking for the specific programming code, or signatures. of known viruses. They also look for common behaviors of viruses. To avoid conflicts, you should use only one anti-virus program at a time.

Another excellent program, which can be used in conjunction with anti-virus and other security programs, is Spybot Search & Destroy, program that removes spyware and other malware.

It's a superb example of international altruistic entrepreneurship.

The program is written and supported by German software engineer Patrick Kolla and the volunteers who work with him, and it's distributed by Kolla's Irish company Safer Networking Ltd. The program, which has won many awards for its effectiveness, is free for noncommercial use, supported by donations. Fees for corporate use depend on the size

Reid Goldsborough  |  Contributing Writer
Reid Goldsborough is a syndicated columnist and author of Straight Talk About the Information Superhighway. He can be reached at reidgold@comcast.net or www.reidgoldsborough.com.