Microsoft released a statement Saturday claiming that the attack--which infected an unknown number of IIS servers, which, in turn, delivered malicious code to any Internet Explorer user who surfed sites hosted by those servers--"is not a worm or virus. In other words, this attack is a targeted manual attack by individuals or entities towards a specific server."
Symantec's Corp.'s research, said Oliver Friedrichs, a senior manager with the company's virus response team, also leans toward manual hacks. "That's what it looks like," he said. "It's certainly not a worm or an automated exploit."
Microsoft said that all the compromised servers were running IIS 5.0 unpatched against a vulnerability disclosed in April. Some security firms last week theorized that even patched IIS systems were vulnerable, but that now seems to have been a false alarm.