The Conficker worm managed to infect about 800 computers at the University of Utah last week, prompting the school to block Internet access temporarily to contain the infection.

The worm is believed to have gained a foothold on the university's network through an infected USB device, said a spokesman with the university's school of health sciences.

He said that IT personnel believe no data was stolen as a result of the infection. "We think we caught it early," he said.

The university has posted tips for curing Conficker infections. Conficker only affects computers running Windows.

The main attack vector used by Conficker is a vulnerability that Microsoft patched in October. But because many organizations and individual users do not keep their software up to date, the worm spread, infecting almost 9 million computers by January. Currently, Conficker infections are estimated at about 1 million to 2 million computers worldwide.

The creators of Conficker have revised their malware several times, adding new infection vectors and new capabilities. The worm also can spread through weak administrative passwords, which it attempts to guess using a password-guessing attack, and through USB devices.

Conficker tries to copy itself to removable media drives in a way that forces code execution whenever the removable drive is inserted into a computer system. It also employs a social-engineering attack, in case the Windows autorun program has been prevented from working automatically: It names the autorun.inf file "Open folder to view files," which typically tricks users into running the malware by clicking on it as if it were a folder.

In February, Microsoft offered a $250,000 reward for information leading to the arrest and conviction of those responsible for Conficker worm. To date, no arrests have been made.

The first iteration of the worm, Conficker.A, makes an effort to avoid infecting systems in a Ukrainian domain or using a Ukrainian keyboard layout, according to a report by SRI International. This suggests that the creators of the malware may live in that part of the world and may be exempting their home country to avoid attracting attention from local authorities.

Last week, a new .E variant was detected by Symantec. It attempts to update Conficker.C with new capabilities, spamming malware, and rogue antivirus software.

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