An up-to-date Internet security package is the best defense against Conficker, the malicious software that prompted Microsoft to issue a $250,000 reward for information leading to the arrest and conviction of the cyber-criminals responsible for it.

Conficker is a "time bomb" computer worm expected to begin doing its damage on Wednesday. The worm can turn home computers into part of a super-spamming system and leave vulnerable personal data. It is reported already to have infected as many as 12 million Windows-operated personal computers worldwide.

Microsoft describes the Conficker home PC threat as "severe" at its Malware Protection Center Web site.

One sign that a computer using Windows XP or Vista could be infected with Conficker is if a security update is blocked for download, said Clayton McCauley, system administrator in the computer science department at the College of Charleston.

Without the latest home PC security, whether a Conficker worm is present is hard to diagnose. "There's not always a clear sign that it's infected," McCauley said.

Up-to-date home PC security can

remove Conficker, he said.

Windows is 90 percent of the home PC market, and the Conficker worm is specific to the Windows system. Apple Macs are not likely at risk, McCauley said.

The latest version of a security-enhanced Web browser is a good defense. McCauley recommended Windows Explorer 7 or the updated version of Firefox.

He also said to turn off the preview pane that automatically opens e-mail. If a message pops up on the home PC screen while surfing the Web that a Web site cannot be guaranteed as safe, it's best to stay away from it, he said.

Cyber-criminals are always prowling for holes in the Windows defense system, so it's important to update your home computer when an alert is issued on the screen that a "patch" is available to counter a new security problem.

The Conficker program grabbed global attention when it began spreading late last year and quickly infected millions of computers with a software code that is intended to lash together the infected machines it controls into a powerful computer known as a botnet.

The existence of the botnet has brought together some of the world's best computer security experts to prevent potential damage, the New York Times reported.

Botnets are used to send the vast majority of e-mail spam messages. Spam in turn is the basis for shady commercial promotions, including schemes that frequently involve directing unwary users to Web sites that can plant malicious software, or malware, on computers, the Times reported.

"This kind of thing happens periodically," McCauley said. That's why a home computer security package is so important, he said. If a worm or other malicious software gets into a home PC, private data such as credit card information and other financial records could be at risk, he said.

McCauley said a powerful botnet offers an enormous amount of computer power that criminals can use for a variety of purposes, including cracking passwords. Most botnets originate overseas, he said. "We have to watch for botnets all the time," he said.

Reach Prentiss Findlay at 937-5711 or pfindlay@postandcourier.com.