DRM = Digital Rights Management I think. It's to do with developers/publishers protecting their digital products. It ranges from something simple like Matrix Games requiring a key to input, to other more draconian measures like limited installs, activation and deactivation and, imo, the king of the hill - STARFORCE.
People are anti-DRM because it means legitimate customers having to jump through hoops to play a game they've purchased.
In nearly all cases, it causes more harm for the legitimate purchaser than it does for the "pirate" cracking the game. as an example, Silent Hunter V. It's DRM requires a constant internet connection. Legitimate purchasers of said game have experienced issues with the server the game has to contact. On the other hand, it's widely accepted that the game has been "cracked" (DRM removed) and "pirates" are playing the game trouble free.
In another example, Silent Hunter IV had some DRM (Fade??) which messed with the graphics and some calculations in the game. However, legitimate purchasers were experiencing these graphical issues and I think 9from memory) the DRM was not activating properly, hence suggesting everyone had a "pirate" version. There was some name calling at the time...to people who had legitimately bought the game. (from what I remember)
Those are two examples and whilst they may not be 100% accurate (my memory is not like it used to be), the examples showcase the issues being forced onto legitimate purchasers of games. Meanwhile, "pirates" pretty much get a DRM free, problem free gaming experience!!
Thank-you JudgeDredd, so I guess Steam is an example of a DRM? Perhaps I should learn to read the small print...
Without wishing to tempt fate, I have had no issues with Steam (although I have only played a few games so far and all of these are in off-line mode).
England expects that every man will do his duty. Horatio Nelson October 1805