What happens if I share my account with somebody else?

You will lose your account for at least a few weeks, maybe forever.

What happens if I try to break security on (or with) a CS system?

You will lose your account for at least a few weeks, maybe forever.

Can I lose my account for other reasons?

Yes, if you abuse the system in a way that isn't specifically forbidden, but is obviously a bad idea, you can lose your account.