Google's deprecated messaging service, Talk, appears to be experiencing some major issues as of late. The service has been erroneously sending messages to the wrong recipient, and many times to Talk users who are not on your contact list. The cause of the issue is not very clear at the moment, but thankfully there is a fix that is easily deployable.
Anyone using Google Talk can bypass these errors by simply downloading and installing Google Hangouts, the messaging service that has replaced Google Talk for several months now. When Google first began receiving reports about the error, it said that it immediately dispatched a team to investigate and as of this writing, things appear to be back to normal. I suggest installing Hangouts anyway. I have used the service for months and like it much better than the antiquated feeling Talk messenger.