Freezing Temp, Spirit Box, Fingerprints.Strength:
Can travel through doors and walls, but most importantly, can see through any door (that includes locker doors)Weakness:
Salt. A wraith stepping into salt increases ghost activity and, according to the wiki, stops him from attacking. (I never observed the latter part, though) Secondary Evidence:
Very high Activity after stepping into salt and being smudged multiple times. Rarely steps into salt and never leaves footprints (due to flying). Rarely produces a footstep sound. Hunts you through closed doors. Technically can go through walls, but I personally never actively observed that.
These boys are dangerous, be it with their ability to see through doors alone. So hiding behind a door like in a locker or a small storage room will not help you one bit. Get a wall between you and the wraith, should he hunt you. According to the wiki, they stop attacking (I assume hunting) when they step into salt, but I have yet to observe that. It might be because they also fly over the salt most of the time.
It also is important to note, due to their ability to fly through walls, it might be that adjacent rooms might also get colder, especially if it is in a large map with many small rooms (e.g., the asylum), so double check your rooms which one might be the ghost's room.
Apart from that, they can get extremely active if you use all the smudge sticks and salt does your disposal, easily surpassing any Oni you might find in the field.
A small disclaimer here, I have seen wraiths leave footprints, but this is rare and most likely a bug.