These may seem simple and obvious, but here are clues that your Google account may have been hacked.

1. You received dreaded security alerts from Google.
2. your inbox has emails indicating you changed your password.
3. Your outbox has emails you know you did not send.
4. Your password has changed, and you know you did not change it.
5. Your security setting has been changed.
6. Your contacts receive emails you know you did not send.