Microsoft reported a significant increase in the number of infected users over the weekend, and researchers at Trend Micro estimated about 6,000 sites had been infected. The move is a shift in tactics for hackers, who had been relying on rogue Web sites to propagate their malware.

"Based on our stats, since the vulnerability has gone public, roughly 0.2 percent of users worldwide may have been exposed to Web sites containing exploits of this latest vulnerability," according to a posting on the Microsoft Malware Protection Center (MMPC) blog. "That percentage may seem low, however it still means that a significant number of users have been affected. The trend for now is going upwards: we saw an increase of over 50 percent in the number of reports today compared to yesterday."

So far, the compromised sites have run the gamut, ranging from a popular search engine in Taiwan – now reportedly clean – to various pornography sites. 

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