They also had that nasty episode with piracy a few years back and as far as I understand they are still clinging to a YouTube model where it's up to people to report that content is pirated -- but you need a Udemy account to do that, something not all content creators feel like creating especially. Here is Rob Conery's blog post about this episode:

https://medium.com/@robconery/how-udemy-is-profiting-from-pi...

I don't know if Udemy fixed this or just made it easier for creators (and others) to flag pirated content but I haven't heard about this problem for a while.