More than 50,000 webpages have been compromised in an SQL injection attack that has been dubbed Lizamoon.
Security firm Websense has been tracking the attack since it first appeared on March 29. The attack exploits a security flaw and allows hackers to insert a link to their website into the URL.
Subsequently, web users are redirected to the hacker's website, which features fake antivirus software and claims their machine has been infected with malware and they must download a program to remove the malware.
Websense gave the attack the Lizamoon monkier after the first domain it saw web users being redirected to on March 29.
The security firm also believes sites using Microsoft SQL Server 2003 and 2005 are the only one being attacked. However, websense said it was unlikely there's a vulnerability in Microsoft SQL Server 2003 and 2005, and the flaw was more likely to be found in the web systems used by the sites.
"The LizaMoon mass-injection campaign is still ongoing and more than 500,000 URLs have a script link to lizamoon.com according to Google Search results," Websense said in a blog.
"All in all, a Google Search reveals over 1,500,000 URLs that have a link with the same URL structure as the initial attack."
Websense said the attack could carry on for some time. "We're still seeing references to Gumblar, which was a mass-injection attack found in 2009," the security firm said.