If installed, up to five adware programs could have landed on the users' computers. La Pilla contacted MySpace but the company's defense team had already taken the ad down and was working to find its source.

Any user that was browsing with Internet Explorer and had not installed the latest Microsoft patches was vulnerable to this attack. In January, Microsoft released a patch that prevents WMF (Windows Metafile) files, so users that had installed the patch were safe. Browsers using Firefox version 1.5 or later are also protected from WMF files.

iDefense estimates that the ad was served to MySpace, Webshots, and possibly Facebook, installing the malware on 1.07 million computers.

MySpace executives were not available for comment, but Hemanshu Nigam, chief security officer for MySpace, issued the following statement:

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