If on my forum I select 'Who's Online' and then look where it shows a guest as logging in, then click on the IP and there are lots of 'Password Incorrect' - showing member names, is it likely that these are web-bots trying to log onto the forum?
This is a widely known issue going on at the moment, and yes they are bots slowly trying to find out usernames and passwords.
This topic probably has the most discussion on this so far Being logged out by bots trying to log in (http://www.simplemachines.org/community/index.php?topic=416928.0)