Cryptome.org, a website dedicated to disclosing confidential information, was compromised last week and was used to infect PCs running Internet Explorer through drive-by exploits.
The security breach was discovered Sunday when a reader notified Cryptome's owners about a security alert he received from his antivirus program when accessing the website.
A subsequent investigation uncovered that a rogue script element had been injected into the website's HTML pages on Feb. 8 in order to direct visitors to an installation of the Blackhole exploit kit.
The Blackhole exploit kit is commonly used to launch drive-by download attacks from compromised websites by exploiting vulnerabilities in programs installed on the computers of users accessing them.
In Cryptome's case, the Blackhole installation targeted unpatched versions of Internet Explorer 6, 7 and 8. A log file found on the server suggests that 2,863 different IP addresses were targeted until the rogue script was identified and removed.
In order to avoid detection the attack code filtered out connections from Google, the University of California at Santa Barbara, and several online website scanning services.
It's not clear how Cryptome was initially compromised, but researchers who looked at its Web server found that it was running an outdated version of FrontPage extensions.
"Frontpage hasn't existed for quite some time and the web server extensions that support it have been buggy and had many security vulnerabilities from day one," said Chester Wisniewski, a senior security advisor at antivirus vendor Sophos, in a blog post.
Wisniewski's recommendation for webmasters is to disable any Web server modules that are not used in order to reduce the potential attack surface. Turning off debugging and status pages is also a good idea, because these tool can give attackers hints about where the vulnerabilities might be, he said. Wisniewski's other advice include using a version control system that can monitor changes made to websites and regularly reviewing the server access logs for suspicious activity.
Internet users should keep their software applications up to date in order to be protect themselves against drive-by download attacks, he said. The operating system, browsers and browser plug-ins are some of the most frequently targeted pieces of software.