Experts: more sophisticated Windows worms likely

"They were clueless," said Maiffret. "A real worm writer with any type of skill wouldn't have needed to connect back (to an infected machine) in order to get infected."

Ullrich agreed, calling Blaster's infection method "a bit primitive" and pointing to the worm's habit of stopping after it scans only 20 or so machines to check for infections.

"Code Red scanned 100 or 200 machines at a time," he said, referring to the devastating worm of 2001.

Maiffret, Ullrich and others agree that future versions of the Blaster worm are likely, as are new worms that exploit the RPC vulnerability.

Those variants might patch the holes in Blaster's code or modify it, for example: redirecting the worm's programmed DOS (denial of service) attack against Microsoft's windowsupdate.com site to a different Internet domain or IP (Internet Protocol) address, Maiffret said.

The Internet Storm Center had not received reports of any Blaster variants Tuesday, Ullrich said.

Despite its many faults, Blaster did do one thing right, according to Maiffret and others: target an easily exploitable and ubiquitous security flaw that affects home users more than just closely monitored servers.

"Even as poorly written as (Blaster) is, it's still having an effect and we're seeing a lot of impact from the worm right now. That's really the scariest part," Maiffret said.

And the worm's programmed DOS attacks against Microsoft could still cripple the networks used to launch the attack, even if they don't bring down the Redmond, Washington software company's Windows update servers, Maiffret said.

Like any worm, Blaster will also be hard to eradicate, according to Mikko Hyppönen, antivirus research director at F-Secure.

"We're still fighting Code Red from 2001, so (Blaster) will keep spreading for a very long time. I expect it will still be scanning networks in 2005," he said.

In the end, however, the emergence of a serious -- but not devastating -- worm like Blaster might help inoculate the Internet community against future variants that are more virulent, spurring users to patch vulnerable systems and install other protective measures like firewalls, Maiffret said.