Security Number

[Drackard]

Basically, i want to get another game off Steam using my Visa, however the security number on the back (on the signature strip) has worn away. I think i remember it as i knew most of my details off the top of my head, however if i enter what i think it is and it's wrong, does Steam let me know and not give me the game or does it lock my account or something .. just a bit confused.