SecuROM ?

SecuROM = DRM. You already answered it yourself.

It's not hard

SeruROM is a third-party product, not Steam related at all. It's copy-protection for media like CD's and DVD's. It requires a driver be installed on your system, many people have problems with it since it alters how the drive functions in many cases and has been known to bork drives in older versions because it requires the drive read portions of the disc not normally accessed. With keys, online authorization, this kind of DRM is no longer the vital stop-gap it once was for thwarting piracy.

tl;dr I avoid it like a stripper with herpes.

third-party means not steam. you and steam are the first and second parties here, so a third party is someone else. steam is already drm, as you need to have the game on your account to play it. i won't buy (or even enter giveaways) for games that have third-party drm. i make an exception for series i got into before making this decision, such as assassin's creed.

securom has been around a long time. it used to be a disc copy prevention system where software could tell if the disc in the drive was a copy, but of course that wouldn't apply to downloaded games as there's no disc. the worst it's been (as far as i know) is an online activation system than installs alongside the game (and isn't easily removed, even if you remove the game) and checks every so often (definitely the first time you run it on a "new computer") to make sure you're allowed to run the game. steam does basically that already, but securom takes it a step further and can limit you to a number of installs. the details aren't clear but i've heard changes as simple as upgrading your video card makes securom think you're a different computer and uses up another install. once you're out of installs (and the only way to find out about this is to try to use another one once you're out), you have to buy the game again if you want to keep playing.

i have the non-steam version of spore, which has a 3 or 5 install limit securom. they eventually released a deauthorization tool so you could supposedly get back the install from the computer you ran the tool on, so you could reformat it or move the game to a new computer. i haven't run into any actual problems and am inclined to believe the installs eventually expire because i'm sure i've installed it more than the limit even if you subtract the times i ran the deauth tool.

still, the limited install drm is the worst out there for me. i see a lot of people upset about single-player games requiring an internet connection just for drm purposes (i don't know if securom also does that), which is of course worse than no drm but rarely inconvenient to me since i almost always do have an internet connection.

a list for you to read!

OR you know, you could have taken the first sentence in your post and Googled it.

I think they removed that from Far Cry Complete Pack.

SecuROM is cancer. Worst DRM ever.