The SANS Institute has uncovered what they've termed a "rare gem" as far as computer security investigations go that sheds new light on how up to 20,000 Web sites have been hacked since January.

They found a sneaky software tool that uses Google's search engine to hunt for Web sites running certain kinds of vulnerable applications, wrote Bojan Zdrnja, on the institute's blog.

"While we had a general idea about what they do during these attacks, and we knew that they were automated, we did not know exactly how the attacks worked, or what tools the attackers used," Zdrnja wrote.

When the tool finds a site that is vulnerable, it kicks into action. "The exploit just consisted of an SQL statement that tried to inject a script tag into every HTML page on the web site," Zdrnja wrote.

That SQL statement was crafted to target Web sites running Microsoft's Internet Information Server and SQL Server. Once compromised, the Web sites were then rigged to serve malicious software to visitors using JavaScript, which tried various exploits based on known software vulnerabilities.

Among the malicious programs served up was a password-stealing program for the game "Lord of the Rings Online," security vendor McAfee said last month.

SANS said the software tool also reports to a server based in China, a feature that may be used to count the number of infections in order for the person using the tool can get paid, Zdrnja wrote. The tool may have other functions, but SANS is still analyzing it.

Among the victims from these attacks were the Web sites of security vendor Trend Micro as well as CA.