Suspicious Activity Issues

All of a sudden, as in it's never happened before, I have had three lockouts due to the "suspicious activity on my account" in the space of two hours (while actually playing - I get booted off and the message displays), two of these after running a complete scan on my PC with a couple of anti virus tools and finding nothing. I have a mobile authenticator on my account.
The "suspicious activity" which actually is not in my opinion seems to be triggered at the exact same time as my Norton 360 Premier Edition runs an update - at least all three I've noticed a Norton definitions update had just run. I'll set this to run at greatly longer times and it's possible it's not related, however I'd be interested to know what triggers this "suspicious activity" (probably a trade secret), but clearly (and it hass to be automated) the bot is picking up something when it should not. Very frustrating - any ideas?