LinkedIn, the world’s most popular professional social network with 238 million users, is facing a lawsuit for allegedly hacking into its customers’ third-party email accounts.

The suit claims the company illegally accessed the accounts to get its hands on users’ email contact lists for marketing purposes. It also accuses LinkedIn of using its members’ identities in marketing emails—those personalized “invitations to connect” that you may have seen in your inbox—without their permission.

Anyone who registers for LinkedIn has to give the site a third-party email address, but it’s unclear how the company is siphoning contact lists from those addresses without the account passwords. One possibility: LinkedIn members may be using the same passwords for LinkedIn and their outside email accounts.

Another, much more sinister possibility suggested by the plaintiffs: Linkedin actually has hackers on staff whose job is to access members’ contacts.

According to Bloomberg, the lawsuit points to a LinkedIn engineer’s profile page, where he describes his job as “devising hack schemes to make lots of $$$ with Java, Groovy and cunning at Team Money!”

LinkedIn, for its part, says it will fight the lawsuit. Part of the company’s messaging for new users says, “We will not e-mail anyone without your permission.”

Now, LinkedIn will have to prove that in court.

H/T Slashdot | Photo via tychay/Flickr