There have been a series of posts to NANAE (news.admin.net.abuse.email) usenet group.

Several posters have claimed that they had created unique e-mail addresses strictly for communicating with Ameritrade.

They reportedly started getting spam'd stock trading tips.

in their posts, they claim that they contacted Ameritrade which either denied a breach or told them that there was an "ongoing investigation".

Recently another poster pointed to SEC quarterly filings which indicate that there was a class action lawsuit filed earlier this year and they suspect that Ameritrade only came forward because of the case.