As Lizzie has rightly said, expiration date must be checked up-front, before using it, because sometime it is too late,,,,,,, second, appeopriate size, type, handling and storage conditions are also important to ensure your personal protection is in good shape to do its job,,,,,,,,,
As long as condom did not fail, it provides you protection. No then there is no chance for you to get infected.
Saud ! One point you must keep in your mind, validity of condom protection turns void immediately the monment it fails, and the category of your sex suddenly changes from safe to unsafe with the breakage, irrespective of the duration you were "in" after failure, because they normally tear apart exposing the crown of your tool right in the middle of "hot waters". Key words are, use em correctly and consistently.
If your condom ever failed, while involved in sex with someone of unknown status, you need to get your self tested after the specified period,,,,,
it's always good to check the expiration "before" having sex...
a condom that is expired looses it's integrity and can potentially fail (bust, rupture). if this does not happen...you are protected.