This pie chart shows the different threats that can come from visiting Web sites that advertise unauthorized content.

(Credit: McAfee)

It's common knowledge that you can catch computer viruses on porn Web sites. But did you know it's also risky to surf the Web searching for free movies or music?

A study from McAfee to be released on Tuesday finds that adding the word "free" when looking for entertainment content in search engines greatly increases the chances of landing on a site hosting malware.

For instance, searching for free music ringtones increases the chances of hitting a malicious site by 300 percent, according to the report, "Digital Music & Movies Report: The True Cost of Free Entertainment." (PDF)

Searching for "lyrics" for a particular artist is twice as risky on average as searching for "ringtones" for the same artist for the first five pages of results, the report found.

And including the term "MP3" increases the riskiness of music searches in general. There has been a 40 percent increase in the number of Web sites that are delivering infected MP3 files or that seem to be built for purposes of financial fraud or delivering malware, according to the report.

Meanwhile, McAfee found malware associated with a number of Web sites around the world advertising free downloads of sports games, movies, and TV shows.

Twelve percent of sites that distribute unauthorized content are distributing malware, and 7 percent of sites offering unauthorized content have associations with cybercrime organizations, the report concluded.

"The sites often look very professional and attempt to lure the user with the idea of a 'trial period' or even some nominal fee that is much less than what may ultimately be charged," the report says. "Once the user agrees, they have to authorize their computer to access and interact with computers that are involved in a wide range of schemes--from money laundering to stealing credentials such as user names and passwords. In addition, with this access, your computer is profiled--with all of its software versions, user agents, and any other date--and this information can be provided to third parties for malicious purposes. (This is often called 'fingerprinting.')"

To reduce the chances of landing on malicious sites, McAfee recommends avoiding the use of the word "free" in searches for entertainment content, avoiding clicking on links in banner ads on content sites that aren't well established, not clicking on links posted in forums and on fan pages, keeping security software up to date, and using safe search plug-ins like McAfee Site Advisor that warns of potentially risky sites.