In the hit Broadway musical Avenue Q, the puppet Trekkie Monster sings the X-rated show-stopper, "The Internet Is For Porn." Congressional investigators confirm what Trekkie Monster and most Web surfers know--you can easily find porn by using the popular search engines Google and Yahoo.

Filtering technology used by Microsoft's MSN search engine, however, more effectively blocks pornographic and erotic images than filters used by Google and Yahoo, the Government Accountability Office said in a report issued Monday.

The House Government Reform Committee asked the GAO to determine how easy it is to access pornographic files on popular peer-to-peer programs and the risk of inadvertent exposure. In conducting the examination, GAO looked at Google, MSN, and Yahoo, and how well they filtered requests for hard-core content.

MSN uses a filtering system similar to the one used by the peer-to-peer file-sharing program Kazaa, which identifies titles and metadata to effectively block pornographic and erotic images. Yahoo uses a system that requires users to designate specific words to be blocked, which GAO contends still lets porn sneak by. The GAO did not provide details on Google's filtering technology but said it was not as effective as MSN's system.

"When searching Google using a known search word, we were able to download 79 images, of which 11 were adult erotica," Linda Koontz, GAO director of information management issues, wrote in a 74-page report. "Similar to [peer-to-peer site] Morpheus' filter, Yahoo's filter was largely ineffective in blocking pornographic and erotic images."

GAO used search words that juveniles would likely use to seek pornographic images. GAO didn't identify what were those words.

According to three popular file-sharing Web sites GAO investigators visited in February, 134 peer-to-peer programs are available to the public. Pornographic images are easily shared and accessed on the peer-to-peer programs Warez, Kazaa, and Morpheus, the GAO found.

Kazaa filtered words found in titles or metadata, and Morpheus required the user to enter the specific words to be filtered. The GAO says Kazaa's filter was effective in blocking pornographic images in its searches, but the Morpheus filter was largely ineffective in blocking pornographic content associated with words entered into the filter. Warez did not provide a filter.