jesski,
i'd wait to do your security check until they actually want to employ you. I have forked out $$ a number of times for a check and never got a job with them. The security check is for your asic card, and if you don't get a job, you don't get an asic therefore you should get your money back. I've never seen a dime! They owe me nearly $200, which i'm sure i'll never see!
so yeah - wait!