Mr Georgi Guninski of Bulgara published his "high risk" advisory of the exploit on Wednesday, warning of a security vulnerability in which a malicious person could read files and URLs after enticing someone to view a Web page or read an HTML message that the malicious person created.

"It's definitely a high risk," said Mr Elias Levy, chief technology officer for SecurityFocus.com. "We assume that the only thing people can do is read files-that's pretty damaging in and of itself, but at least for now people aren't able to write or execute programs through your machine. They can only read files from your machine or read Web pages."

Mr Levy added that a hacker could also get into someone's computer system by delivering an e-mail of a Web page to someone who uses Outlook or Outlook Express.

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