It's not Curse (as you guessed by your friends not being banned). Riot actually has Curse installed on a lot of the computers at their office, so if it was just Curse there'd be a lot of Rioters banned as well.
The big thing is to find out what's different with your account than your friends that didn't get banned. Some people have their accounts compromised without them knowing (happened to a friend of mine recently) and those hackers can be the ones using the scripts. A few of the people I've talked to who were banned had macros on their computers that they used with other games, which might be a cause too.
One thing you know for certain though, it's not common software (voice chat, recording, streaming software, etc) that got you banned.