Bruise like mark on LCD screen, just appeared out of nowhere

[TWiST]

So I go to my memory screen and all of a sudden out of the blue I notice this like bruise like dark spot on my screen in the white area, I just got this phone, but I bought it off ebay and It was not there just a few hours ago. I am furious about this it just happened out of nowhere I didn't drop the phone I didn't knock it or anything I don't know what to do if I can send it on for warranty with HTC or if I have to get total protection with sprint and then send it in and how much is that going to be 50 or 100 dollar deductible ?

Any advice would be great, I seemed to have made it a bit smaller by rubbing hard on the screen but I cant get it to go away.