Make a test that they have to pass about a subject, such as Linux, with a time limit. After the time limit, their IP is banned. Make sure you ban all data center IPs, and Tor, and VPNs. Bots may be blocked as well if you block data center IPs, but who cares.
The time limit is so they have less time to search the internet for answers. So make it 10 minutes or less. If you want to just ban everybody, make it one second.
If you make it about programming, a dumbass will have an even harder time searching for answers.