What could be more innocuous than downloading a screensaver to dress up your PC? "Well, the reality is that screensavers are some of the riskiest pieces of software that you can download to your computer," says Shane Keats of McAfee, Inc., makers of a variety of PC protection software.

Keats says that while serious techies know they shouldn't download screensavers from the web, there are 15 million screensaver web searches each month. Those who end their search with a download are likely to find adware, spyware or worse tagging along for the ride.

McAfee found the most dangerous screensaver this summer was Miami Vice and that sites offering baseball or World Cup soccer downloads also were high on the risk list.

Sadly, some of the biggest targets for screensaver foul play are cartoon characters. McAfee looked at 318 kids' TV programs to see how risky it was for kids to download their corresponding screensavers. We're talking Rugrats, Powerpuff Girls, SpongeBob, and Mighty Morphin' Power Rangers here.

After doing a Google search with the character name and the word "screensaver" (precisely the way most families would look for a screensaver, says Keats), McAfee determined that at least 50 percent of the sites listed on the first page of all of these search results were risky sites to visit. Topping the list as worst offender? Mighty Morphin' Power Rangers, where 80 percent of the search returns included links to risky sites. The complete results are documented on the SiteAdvisor blog.

This doesn't mean the Power Rangers have done anything wrong. It just means that unscrupulous web sites have chosen to enact bad practices using the characters' names.

Here's an in-depth example to show you how it works.

A search for "Power Rangers screensaver" leads to all sorts of different web sites, including Starpulse.com (a celebrity web site that uses Screensavers.com as a part of its service). Every time a Starpulse user installs a program from Screensavers.com, Starpulse earns an "affiliate" commission. At the same time, Screensavers.com bundles an adware program called Starwave and a tracking program called Relevant Knowledge, all unbeknownst to you. Your data is now being compromised, and you're being barraged with pop-up ads, too.

To play it safe? Don't download screensavers. If you feel you have to, don't download them from anywhere but the biggest, most reputable sources. For the kids, if Nickelodeon or Disney or another well-regarded brand doesn't make the screensaver available, then stay away.

McAfee's research stems from its work with SiteAdvisor, a program that uses simple color coding to tell you whether a site is safe or risky. To create the rating, the company has robots that search the entire web, logging on to sites, filling out registrations, downloading software, and more. They then monitor what happens to the robots as they use the site. Do they get junk mail? Viruses? Pop-ups? Is it a perfect science? Probably not, but by offering this tool as a free download (or as part of McAfee Suites) and by making data like the screensavers report available, they're certainly helping make the web a cleaner place.