i was gifted portal 2 by someone i don't even know. i don't know if i should be concerned or happy.
The responsible thing to do would be to decline it since it was probably supposed to be destined to someone else.
I suspect in wake of this Valve is going to cancel all transactions made during that time.
Or they might just sweep it under the rug. That will bring a lot of bad PR to them though since they won't be taking any responsible action to fix any possible unauthorized actions made on people's accounts while that bug was occurring.