But could be bots operating from an infected PC in that company. They just don't know it's doing it. See if the IP matches any of your accounts.
Not something I would overly concern myself with if it was my site. If the permissions are right and they can't see anything they won't make any progress. They don't even know what the forum might be, just that they can't see it. Could easily just be a trash forum.
The forum didn't work at all anymore and I had to install a backup.
Once they apparently hacked my server account and uploaded a huge file. But that was the Confixx server and phpBB 3.0.12. I only noticed it when I changed the server. This file was so well hidden in one of my other files that I never had to use.