"Problem":Getting signed in on so many PCs

[hmwere]

I usually sign/log in to my account on different PCs and sometimes forget to sign out.
This has happened on so many occasions. Recently i logged into my account using someones laptop who later traveled off to some place far. I worry that these people might access my account without my permission.
How can i prevent this now that i can not recall any of them well.
If i log off on my PC and log back in, it does not help at all. On their machines i stay logged in!!! Computer gurus please help out regarding this matter.
Is there any other advanced way of logging out completely from all these PCs so i can only log in using my PC? , whether remotely?

[visu]

hmwere,

I usually logged off while come out. In your case you can change password from your end.
Hope it helps.

Regards,