Battle.Net authenticator (I know, it should be on battle.net, not here. please read)?

I cant put a post on battle.net cause it wont let me. I know why though so thats not the problem. The problem is with my authenticator. I noticed today when i logged into StarCraft 2 that my mobile authenticator accepted past codes. For example if I typed in the authenticator code, waited until the next code came, then logged in, it allowed me to log in. Is this normal? If not, what should I do? I feel like some kinda virus or hacker did this.