The website Songsrpeople.com looks a lot like other amateur-video sites. It is wallpapered with clips featuring "the most insane amusement park ever" and "your girlfriend's six friends."
The site draws tens of thousands of visitors a month, according to audience measurement firms. It also has ads for national brands, including Target Corp., Amazon.com Inc. and State Farm.
But Web-security investigators at a firm called White Ops contend that most of the site's visitors aren't people. Rather, they are computer-generated visitors, or "bots," designed to fool advertisers into paying for the traffic, says White Ops, which has blacklisted the site—and thousands more like it—so that ads from clients such as Zipcar don't land there.
An anonymous representative for Songsrpeople declined to discuss the site's traffic but in an email called the White Ops methodology into question.
State Farm said it was looking into the matter while Target declined to comment and Amazon didn't immediately respond to requests for comment.
Authorities and Internet-security experts say tens of thousands of dubious websites are popping up across the Internet. Their phony Web traffic is often fueled by "botnets," zombie armies of hijacked PCs that are controlled from unknown locations around the world, according to Internet security experts.
The sites take advantage of the simple truth that advertisers pay to be seen. This creates an incentive for fraudster...