How to detect and remove a botnet virus from a computer?
Malwarebytes?
Not going to be too effective, most botnets will disable anti virus and spyware. Couple that with constantly changing binaries and a large portion of antivirus software wont stand a chance.
Wouldn't I see it, when my anti-Virus Programm is disabled?
Yes in that case if it was simply turning it off you would see it but there are other ways of disabling anitvirus' without just turning it off. The main defence by botnet operators is more in the second half of what I said in regards to changing binaries, multiple types of malware and general slowness of some antivirus vendors to update their definitions. Not really the place to start talking about techniques etc but some googling will bring up some articles such as this;
https://blog.damballa.com/archives/374