Update: Google says the issue has now been resolved.
Original story: Google Talk — the service behind the company's Hangouts messaging platform — appears to be experiencing a fairly major issue this morning, as some users report messages being delivered to unintended recipients. Reports from Twitter suggest that in some cases messages are being routed to users outside the sender's contact list, presenting obvious — and quite serious — privacy and security concerns.
For its part, Google has updated it service status page to indicate it's investigating an issue with Google Talk, so hopefully the issue can be resolved before too long. In the meantime, you might want to avoid typing anything too private or incriminating into a Google Hangout chat window for the next few hours.