Similar stories from a Google search indicate that it's from incorrect password entries. He can get around the absurdly long time by putting it into DFU mode and then restoring in iTunes.
How the heck did someone have the time to incorrectly input your password? 5,403,985 minutes comes out to 10.275 YEARS....your only quick way is to put the iPhone in DFU mode and re-sync everything. Hope you backed it up.