Thousands of Websites infected by a new Web attack during the past few days won't necessarily be safe even after they remove the offending code.

"People are recommending that the Website remove the link, but that's not enough. If it has compromised your machine once, it will do it again. We've seen evidence" of this, says Roel Schouwenberg, senior virus researcher for Kaspersky Lab, which first discovered this new wave of Web attacks late last week.

The SQL injection attacks, which appear to originate from China, appear to have peaked yesterday, according to Kaspersky. Among the infected sites found by Kaspersky were Travelocity.com, countyofventura.org, and missouri.edu.

It isn't likely, however, that the attacks will reach the volume of SQL injection attacks from earlier this year, which numbered in the hundreds of thousands of sites, mainly because the new attacks are mostly using a new, stealthier, and more closely guarded SQL injection toolkit, says Don Jackson, director of threat intelligence for SecureWorks. Jackson and his team have been in communication with the Chinese developer of the tool, hoping to procure a copy and reverse-engineer it.

"This new SQL injection tool follows the same attack vector as the previous tool the Asprox botnet used," Jackson says. "But this tool is more stealthy and doesn't hammer away at sites...it's a little under the radar."

The toolkit is protected with a layer of digital rights management and appears to be sold mainly in China.

As of Monday night, Websense had seen 1,200 Websites all over Europe, the U.S., and Asia, serving up the malicious code.

The attackers appear to be after passwords, but not just for online gaming as in previous widespread SQL injection attacks. When a user visits a site infected with the attack's signature malicious JavaScript code, he gets invisibly redirected to the attacker's page. The attacker then exploits any third-party application vulnerability in Flash or other browser plug-ins used by the victim, infecting the victim's machine with a Trojan downloader that steals passwords from the user -- from World of Warcraft and other Website credentials to email accounts, Kaspersky's Schouwenberg says.

"The vast majority of users won't see anything," he says. "They see their favorite Website, and everything seems fine and dandy."

Dan Hubbard, CTO at Websense, says the payloads vary, but many attacks appear designed to grab World of Warcraft credentials. "They do appear to have other capabilities, however, that allow them to update, disable AV, and...install more generic password stealers that could be used for a plethora of things."

And this won't be the end of mass Web attacks via SQL injection: "We'll see some big attacks again in the future," Schouwenberg says.

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