Can we play a fair game without the game being hijact

I played couple of games where just before I am about to checkmate my opponent, pieces start moving without I selecting them. Five moves where made in less than a second. I wonder what is going on. A suggestion, Lichess should insert 2 second delay per move and stop the pre-selecting a move, if lichess want to make the game Fairer. I wonder who and how this is happening and who is hijacking the game.

You might have left some computer signed in and someone is trolling you, use this page to sign out from all other computers en.lichess.org/account/security

Thank you flugsio. At security I found this guy twice, deleted one but cannot delete the other.
"27.99.12.38 Australia > New South Wales > Blacktown
Mozilla/5.0 (Windows NT 10.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.103 Safari/537.36
16 days ago [CURRENT]"
How can I delete all. Thanks again
Thank you

Don't just revoke the sessions, change your password. If he/she is getting into your account, revoking a session would only delay him from logging in again.

#3 You can't delete all, because one of them is your current session. Don't worry about that one.