WASHINGTON - Popular US gadget blog Gizmodo apologized to its readers on Tuesday after being duped by malware masquerading as an advertisement.

"Guys, I'm really sorry but we had some malware running on our site in ad boxes for a little while last week on Suzuki ads," Gizmodo editorial director Brian Lam said in a message at Gizmodo.com.

"They somehow fooled our ad sales team through an elaborate scam," he said. "It's taken care of now, and only a few people should have been affected, but this isn't something we take lightly as writers, editors and tech geeks.

"Be careful, load up some anti-virus and make sure your system is clean," Lam advised.

The New York Times website recently fell victim to a similar attack in which users who clicked on a pop-up box were directed to go to a site that claimed to offer anti-virus software.

The site was itself virus-like, hijacking a Web browser and making it appear as if a scan for viruses is running, the Times said.

Web security firm Dasient estimated meanwhile that more than 640,000 websites were infected with malware and said "attackers are focusing more than ever on compromising legitimate websites and using them to distribute malware."

Dasient, in a blog post on Tuesday, said it had identified more than 52,000 Web-based malware infections in the third quarter of the year.

"One of the challenging things about trying to protect sites from the threat of Web-based malware is that the attacks often evolve very quickly and make use of a number of obfuscation techniques to evade traditional malware scanners," it said.