Adware company Zango profits from copyright infringement, a Harvard researcher charged Monday, after the company claimed that sites serving up links to pirated movies were operating within its rules when they pressed users to install its software.

The sites, Movietvonline.com and Bestcinemaonline.com, list dozens of recent movies and popular TV shows, including the blockbuster "The Dark Knight." That was the film that caught the eye of Chris Boyd, the director of malware research for FaceTime Communications, who last week said he had spotted Zango installation prompts on both sites.

"They want you to agree to install Zango in order to view whole movies, some streamed on the movietvonline site from other sources, others in the form of broken up downloads hosted on file-downloading sites," said Boyd in a post to the FaceTime security blog last week.

"Here's a shot of what appears to be a badly made camcorder (complete with people talking and scrunching up paper in the background) streamed on the site," said Boyd, referring to a screenshot from a portion of "The Dark Knight" viewed via Movietvonline.com.

In a follow-up posting, Boyd reported finding identical Zango installation prompts on Bestcinemaonline.com, which also touts full-length movies. "I'm starting to wonder how many of these are actually out there," he said.

Zango has long been criticized by security and privacy advocates, who have charged that the company distributes adware -- software that pops up advertisements while a person is browsing -- using illegal methods. In 2006, Zango settled FTC charges that it used unfair and deceptive practices to download software to users' PCs by paying a US$3 million fine.

When asked last week whether it approved of Movietvonline.com using pirated content to get users to install its software, the company said the site was breaking none of its rules. "We do not sponsor, [or] partner [with], any site hosting copyrighted streaming content," said company spokesman Steve Stratz in an e-mail. "In this case, [movietvonline.com is] not actually hosting the content. We view services that don't actually host content as if they were a search engine. In this instance, this Web publisher is not violating our terms today."