''This is a complicated, sophisticated attack,'' says Ken Dunham, director of malicious code at iDefense, Inc., a security intelligence company based in Reston, Va. ''This appears to be designed to ultimately steal credit card and identity theft information, which can then be sold... There could be hundreds of thousands of victims at this point.''
Johannes Ullrich of the Internet Storm Center, which monitors Internet threats, reports that his organization has been contacted directly by about 20 companies, so he estimates that 100 or more Web sites have been infected with the hostile script.
While less than Dunham's estimate, Ullrich suspects that thousands, possibly 10 thousand, user machines have been infected.
Ullrich says the threat is waning as most of the infected Web sites already have been cleaned up.
But it's been an attack that had security researchers and some IT administrators up all night beating back the flames and trying to figure out exactly how the attack worked.
''This was very dangerous,'' says Steve Sundermeier, a vice president at Medina, Ohio-based Central Command, Inc. ''It's alarming in that you have large, legitimate corporations being used as a tool. As a user, especially if you're entering credit card information, you expect secure Web sites. Their financial security could be breached. And for the credibility of the corporation, this is a huge problem.''
Researchers would not release the names of the companies and Web sites that were compromised for fear of compounding their problems. Ullrich, however, says the compromised sites included industry associations, banks, brokerages and travel-related sites.
The question now is how were the corporate servers infected?
Researchers are still investigating the attack and have been slightly thrown by reports from corporate administrators who said their machines had been fully patched.
Dunham reports that there is some speculation, even coming from the Microsoft camp, that the breakins and server infections are related to the MS04-11 vulnerability.
''With fully patched boxes being infected, it appears there may be another component of the MS04-11 vulnerability,'' says Dunham. ''There's a whole bunch of stuff in there and some of it is related to the IIS servers... We don't know how they are getting exploited. We're talking about highly secure environments.''
Ullrich, however, says it's possible that the sites were compromised some time ago before the servers were patched.
Microsoft recommends that users run a search for kk32.dll and surf.dat. If either of the two files is present, the computer may be infected. Computers can be cleaned by using up-to-date anti-virus software.