From the New York Times (link):
AMERICAN technology firms are taking heat from the public and Congress for helping China’s government police the Internet. But this controversy extends well beyond China and the so-called Internet Gang of Four: Google, Yahoo, Cisco and Microsoft. Just how many American companies are complicit hit home for me last month when dozens of readers of BoingBoing.net e-mailed us to say they had been suddenly denied access.
The cause was SmartFilter, a product from a Silicon Valley company, Secure Computing. A recent update to the nannyware’s list of no-no sites had started blocking our site as containing “nudity.” This is absurd: a visit to BoingBoing might yield posts about iPod-shaped cakes and spaceship blueprints, but not pornography. SmartFilter’s data managers later told us that even thumbnails of Michelangelo’s “David” could land a site on the forbidden “nudity” list.
See also a video about SmartFilter from Google Currents.