Google sent out a warning to 20,000 websites informing them that their website may be hacked and injected with JavaScript redirect malware.

“[W]e think that JavaScript has been injected into your site by a third party and may be used to redirect users to malicious sites,” said the Google warning.  “You should check your source code for any unfamiliar JavaScript and in particular any files containing ‘eval(function(p,a,c,k,e,r)’. The malicious code may be placed in HTML, JavaScript or PHP files so it’s important to be thorough in your search.”

The Google message also stated that the server configuration files of the websites may have been compromised, which could show cloaking or signs of the infection only in some situations.  Google advises site owners to investigate on the matter, and remove the malicious programs.  They also remind site owners to to keep their security software updated.

Google’s team is constantly keeping an eye on the security of websites.  Last year, the search giant excluded more than 11 million URLs from the “.co.cc” domain, the fourth largest domain in the world, because it was frequently used by cybercriminals to spread rogue antivirus programs or conduct drive-by attacks.

In an e-mail to Computerworld, Google spokesman Mark Jansen stated that the letter of warning is part of the company’s dedication in eradicating malicious programs on the Internet.

“It’s part of our ongoing mission to be transparent with webmasters and do our bit to help prevent spam,” he said. “In fact this isn’t a new phenomenon; we communicate very openly with webmasters and always have done.”