How can I block a computer name on our Watchguard?

I have noticed computer names when I look at the Host Watch on our Firewall that are not any of our company computers.  So it seems as if someone else is gaining access to our system.  I have also noticed the error of getredirname when I look at the traffic monitor. I have seen some of the information posted about that it and it could be a malware.  I am not familiar with the Watchguard and cannot figure out how, when I see a computer name that isn't from our company, to block it.  Thanks for your help.