On-line security? I use AVG because, over the years, all the other major ones I've tried have given me grief of one kind or another. That only applies to me and my circumstances at the time while others have had no troubles --- but it sticks in the mind.
To borrow from a detective who didn't actually exist "when you have eliminated the impossible, whatever remains, however improbable, must be the truth". You haven't tweeted anything rude about Putin (or anyone Chinese) recently have you??
And do you have SL on your phone? Most are too fiddly for the game (IMO) but, I have used mine to log in emergencies. Maybe next time you are locked out you could try it?
And lastly, wait until you have a problem, get on here as soon as you are able and see if anyone else had a problem at the same time and what they were using. Solve the mystery and you could become an SL hero/legend.