Avast is notoriously sucky though
Thing is, I looked on Reddit, and people with F-Secure, Malwarebytes and such are getting the same things. I just want the Steam version to come out already, it's probably just a IP previously used for spreading malware assigned to Agar.io. Also, still better than Windows ****tender.
Just checked Steam Comments, and my suspections were true:
"A few times my friend had a virus blocker pop up and tell them that it's blocking Malware when switching servers. My computer actually became infected and I'm unable to run executable files currently. I believe the two are related and it doesn't seem this is happening to everyone. Just be aware that this is a potential issue with the servers on their end. Could be a big coincidence, but it doesn't seem likely.
tl;dr There may be malware that is infecting peoples computer playing on the website and switching servers."