The person who stole JUSTIN BIEBER'S computer and camera has posted some of his private videos online.

This person goes by the Twitter handle @gexwy . . . and he or she posted two short clips on a YouTube account under the same name.

Neither one is very scandalous.  One has Justin pranking a friend backstage by dumping some kind of powder on him.

The other was taken several years ago, because Justin is a lot younger in it.  It just shows him in a room with screaming girls looking in the windows.

However . . . "Gexwy" also sent a five-second clip to PerezHilton.com that shows Justin at a pool party.

Supposedly, there's more to this clip that will be revealed later today, and it's something Justin wouldn't want anyone to see.