A widespread and dangerous Microsoft Corp. Windows vulnerability, spam e-mail messages and human frailty combined in recent weeks to produce a flood of new Internet worm attacks, according to experts at leading antivirus and e-mail security companies.
August saw four major worm infections alone, according to antivirus company Symantec Corp., making it one of the busiest months for antivirus vendors in recent memory.
"Taken all together, this has been a more intense week, in terms of virus activity, than any we've seen," said Chris Belthoff, senior security analyst at antivirus company Sophos PLC.
That activity included the appearance of W32.Blaster on August 11, a virulent new Internet worm that exploited a flaw in the Windows implementation of the RPC (Remote Procedure Call) protocol, which enables client and server applications to communicate across networks.
The worm spread worldwide in a matter of hours, infecting hundreds of thousands of Windows machines before the outbreak began to wane, according to Internet Security Systems Inc. (ISS) .
A survey of 1100 organizations by TruSecure Corp. found that almost 21 percent were infected by the worm, with 15 percent of corporations worldwide recording a "moderate" or "major" impact on operations by Blaster.
The impact among home users, who are generally less well-protected than organizations, is believed to be even greater, according to Marc Maiffret, chief hacking officer at eEye Digital Security Inc.
As Blaster waned, new worms emerged that exploited the same vulnerability including W32.Welchia, also known as Nachi, which attempted to patch Windows systems with the RPC vulnerability.
At the same time, a new version of the Sobig worm, Sobig.F, began bombarding e-mail accounts around the world, prompting new infections, warnings from antivirus companies and hurried updates of antivirus software.
E-mail filtering company MessageLabs Ltd. of New York City intercepted ten times the normal number of e-mail viruses in the 24 hours after Sobig.F appeared and has intercepted over three million copies of the virus so far, according to CTO Mark Sunner.
But the recent spate of large outbreaks don't herald the arrival of a new and more dangerous generation of viruses, as did the appearance of the Code Red and NIMDA worms in 2001, or the SQL Slammer worm in January, according to Belthoff.
"I think it's an intersection of a couple things," Belthoff said. "Blaster and (Welchia/Nachi) -- those are all opportunistic worms. They're all based on this Windows (RPC) vulnerability. Blaster didn't take any in-depth skill to write."
In the case of the new Sobig worm, improvements in that worm's ability to send out copies of itself in e-mail messages meant that even a small number of infected machines could generate massive amounts of infected e-mail traffic, according to Sunner.
MessageLabs researchers believe that there is a link between the Sobig author and the spamming community and that machines that are compromised by Sobig are being used as distribution stations for spam e-mail, Sunner said.
Sixty six percent of the e-mail messages MessageLabs intercepts come from such machines, commonly referred to as "open proxies." And the increase in spam traffic corresponds closely to the appearance of worms like Sobig, Sunner said.