The company intends to test the service this summer, but beyond that, many details aren't yet known. Such a program might help the site -- but might also expose it to further liability. One critical detail that's still unclear is whether Twitter intends to charge for the service.

If so, it seems likely to create more legal headaches for Twitter than it cures. Consider, a paid verification system will almost certainly result in allegations that Twitter is trying to shake down celebrities for cash, rather than proactively police its service for imposters.

Currently, it's not clear whether Twitter faces liability for fake accounts. Certainly users who create the accounts could face libel or trademark infringement lawsuits -- though they might also have a defense if the accounts are clearly parodies.

But Twitter itself could face liability for at least two reasons. If a fake account violates a celebrity's trademark in his name (and some courts have held that celebrities' names are entitled to trademark protection), Twitter could be liable for enabling that infringement. Web companies are immune from liability for many types of unlawful content posted by users -- including defamatory material and illegal housing ads, to name just two -- but they are liable for posts that violate people's trademark, copyright or other intellectual property rights.

Secondly, Twitter also could face liability for using the phony profiles to promote itself. When Cardinals' manager Tony LaRussa sued the site about a parody profile mocking him for a 2007 drunk driving arrest, one of his allegations was that his name was being used by Twitter to lure others the service. "The site states in large lettering: 'Tony LaRussa is using Twitter,' and encourages users to 'Join today to start receiving Tony LaRussa's updates,'" his lawsuit alleges.

Court records show that LaRussa's lawsuit, originally filed in San Francisco Superior Court, was transferred to federal court on Friday.