Mail stopped working; 100% CPU on clamAV, and can't login to the control panel

As in title.

Mail stops working randomly, and I logged in to see what's happening, to see that clamav is running and is running 4-5 processes all of which are taking ALL available CPU power. I restarted the box, and killed the processes in attempt of a quick fix, but no success.

I tried to log into the control panel by going to

https://my.domain.tld:81/

but when I enter my password and username it throws me back to the same page as I would see while logging in, but with this in the URL:

https://my.domain.tld:81/login.php?err=

mySQL etc are up and running, I have restarted ispconfig, but the problem persists. What could it be?

Any help appreciated!

Edit: Upon killing the clam processes started by one user, more popped up started by other users. Is this some sort of routine maintenance? However it shouldn't be taking 100% CPU AND messing with our ability to log into the control panel right?

EDIT2: I've found this in syslog:

Code:

Apr 14 11:54:40 hosting mysqld[948]: 080414 11:54:40 [ERROR] /usr/sbin/mysqld: Table './db_ispconfig/session' is marked as crashed and should be repaired
Apr 14 11:54:40 hosting last message repeated 5 times
Apr 14 11:54:41 hosting mysqld[948]: 080414 11:54:41 [ERROR] /usr/sbin/mysqld: Table './db_ispconfig/session' is marked as crashed and should be repaired
Apr 14 11:54:41 hosting last message repeated 3 times