If you still got a/the trojan on your PC they most definitely can try to brute force your authenticator code.

Blizzard has no auto-block feature that blocks your IP after you unsuccessfully tried to log in X times.

The chance of them hitting it is about as small as winning the lottery... but they can still be trying ;p

Either way you should make sure that your PC is clean by running decent programs to check it.

Never rely on just your authenticator to keep you safe.