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Site-blocking worm carries phishing risk

Worm alters system files to block some antivirus company Web sites--a ploy that could be used in phishing scams, Trend Micro warns.

A new variant of the Crowt worm could block infected browsers from accessing Web sites belonging to some antivirus sellers, Trend Micro has warned.

Crowt.D, first discovered Wednesday, opens up the Google News site upon infection, then alters the computer's hosts file to add a list of Web site addresses, the antivirus company said in an advisory last week. When people click on one of those addresses, they are redirected to a local loopback address instead, a move that blocks access to the sites in the list. The worm restricts access to antivirus vendor sites including,,, and

Trend Micro has given the worm a "low" risk rating. But Adam Biviano, senior systems engineer at the company, said the worm is noteworthy because it has the potential to send a victim to a phishing Web site even when they have manually typed in a Web address.

Phishing schemes typically use spoofed Web sites that look like they belong to a trusted provider, such as an online retailer, but are actually hosted by scammers. The sites attempt to get people to type in confidential information such as passwords and credit card numbers.

The Crowt.D infection's ability to redirect people from one Web site to another is especially dangerous when it involves an online banking service, Biviano said.

"Banks are telling their customers to type their specific Web site address into the browser. However, if the host file has been compromised, then even if the URL is typed in, the browser will still go to the phishing Web site," Biviano said.

Biviano said the Crowt variant can redirect people, regardless of which browser they use.

"It uses the Windows associations to launch a file, so it will open your default browser," he said. The worm affects Microsoft Windows 95, 98, ME, NT, 2000 and XP, and spreads by sending itself out to e-mail addresses found in the Windows Address Book.

DNS poisoning is another method that is being used by hackers to try to redirect Internet users to fraudulent Web sites. On Wednesday, Microsoft advised customers who use its server software to reconfigure their settings to avoid such attacks.

Munir Kotadia of ZDNet Australia reported from Sydney.