A computer worm managed to snarl hundreds of thousands of machines worldwide in the latest virus-like outbreak affecting the Windows operating system.

The new worm, dubbed Sasser, does not require users to click on an e-mail attachment to activate it, which causes it to spread more rapidly than most viruses.

It was discovered in the US late on Friday and began spreading yesterday as employees returned to work and booted their machines.

The worm caused some computers to continually crash and reboot, apparently the result of bad programming by the virus writer rather than intent, security experts said. Sasser does not cause any permanent damage to files or machines, they added.

Among victims were companies in Britain, Germany, and the United States that are clients of Network Associates, said Vincent Gullotto, a vice president at the company's anti-virus research lab. He would not name the companies.

A large television network in Europe was also hit, two security sources said.

Finland's third largest bank, Sampo, closed 120 of its offices for a few hours as a precaution while technicians updated anti-virus programs. E-banking services and the bank's automated teller machines worked normally.

Delta Air Lines spokeswoman Peggy Estes refused to say whether weekend computer troubles that grounded flights to and from Atlanta for about seven hours were related to Sasser.

Once Sasser infects a computer, it automatically scans the Internet for other computers with the flaw and sends a copy of itself there.

Microsoft recommended that owners of Windows 2000 and XP computers install software patches by visiting http://windowsupdate.microsoft.com. Firewall and anti-virus programs that have the latest updates can also help contain or prevent infection. Sasser does not affect older versions of Windows.

The web sites of anti-virus vendors have instructions for removing the worm from machines already infected.

Security experts braced for additional infections today, when Europeans return from the three-day holiday weekend, but Sasser's outbreak was not likely to exceed that of last summer's Blaster, which had infected millions of computers.

Tuesday May 04, 2004