Update: A Valve employee took to reddit to counter what was said in the bug report:
Hi! Valve employee here. The bug report is incorrect. VAC will not ban you for simply having catbot in your user name (either your steam profile or on one or more of your linux accounts).
The bug report--and I suspect many of the posts in this thread--are a tactic employed by cheaters to try and sow discord and distrust among anticheat systems.
VAC has many different types of detections and we cannot discuss what they do publicly because doing so makes them less effective. However, one thing I can disclose is that all detections require that the detection occur while a user is actively cheating and connected to a VAC-secured server.
Linux historically hasn't been a problem for cheating--the base rate of cheating is significantly lower on Linux than it is on Windows. Unfortunately, a "healthy" community of cheaters grew up around catbot on linux and their impact on TF became large enough that they simply could no longer be ignored. Those banned users are very annoyed that VAC has dropped the hammer on them.
Kisak moderates many of valve's github bug repositories for us in an attempt to keep the bugs high quality and actionable. The VAC team asked him to close the issue in question and to indicate that github was not an appropriate location to discuss VAC bans. He did so, and we support this action.
For proof that I am a Valve employee, you can check my posting flair in the other subs I post on (/r/CSGO and /r/tf2) or a mod can message me and we can work on confirmation using my work email and PMs.
So in this case what Valve is doing is fine. They're getting rid of cheaters and that's how it should be.
Happy New Year! Let's start 2018 with a bit of a joke shall we: Knock Knock. Who's there? Catbot. Banned.
It seems one user came across an unfortunate issue playing Team Fortress 2 on Steam, as they were VAC banned for having their Linux desktop username contain "catbot".
I can certainly understand when a bot comes along, if it uses something so easily identifiable then as a quick temporary solution you could ban it like that until it's fixed. However, that's obviously not a good long-term solution and will (like in this case) cause an issue for users. It's not even a good short-term solution, considering how many millions of possibilities there are for a username to have "catbot" in there somewhere. Going by usernames just isn't a good idea, it's just not. Why is it not? Bots can just use random names, then this doesn't even become a temporary fix, it becomes useless.
This is what Valve replied with:
Good day, I've received word from the VAC team that this is intentional and not open for discussion on Github.
In general VAC issues are not handled on Github in any capacity and further issue reports on this may result in being banned from the Valve Software issue trackers.
Ouch. I get why they don't want their GitHub filling up with VAC issues (it's not the right place after all), but threatening a ban just like that, without any suggestions on what the user could do is a bit harsh don't you think? Considering this GitHub request is talking about bans, to then threaten a ban from the Valve GitHub trackers—come on.
Valve has done a lot of good for Linux gaming and continues to do so, but I think it's still important to highlight issues, even if they are on the stupid side.