Washington The viruslike "Code Red" worm infected computers around the world Wednesday, although the outbreak wasn't as severe as predicted.
"We're still watchful, but for the first time, we're hopeful as well," said Alan Paller, research director at the SANS Institute, a computer security think tank working with the government to monitor the Internet.
He said despite the good news, they had detected new variations of the worm and were working overnight to analyze them and their capabilities.
Almost 150,000 Internet-connected computers running Microsoft's NT or Windows 2000 operating system had been infected by Code Red by Wednesday night, according to SANS data. Although the rate of infection doubled each hour early on, the rate of increase gradually abated.
"We can't say for certain the threat has been eliminated," said Ron Dick, head of the FBI's National Infrastructure Protection Center.
The Pentagon had to shut down public access to many Defense Department Web sites again, a week after it shut down most military sites to protect against Code Red.
A spokesman said the Pentagon system was slowed and one civilian agency's server was infected.
"We remain vigilant in monitoring this situation," said a joint statement by the FBI, White House and other officials Wednesday night.
Unlike a computer virus, which needs a person to help it spread, a worm infects other computers on its own. It does not affect most home computers.
Officials worried that the outbreak would be as crippling as Code Red's first appearance on July 19, in which over 250,000 systems were infected in its first nine hours. As a result, there were widespread slowdowns and outages across the Internet.
This time, after Code Red launched Tuesday, the worm has had a much lower infection rate.