Sure, I've been pranked (old shaving cream on the hand while sleeping comes to mind) and I'm sure I've participated in pranks but none come to mind right now.

HOWEVER, there's a huge difference between a harmless prank and betraying someone's trust to be mean to them. I consider keylogging and pwning someone's machine deep into the in the "asshole" category. I also think that jerking someone's mouse when they are trying to click is not clever, just annoying, not funny. Especially because it could more effectively be done physically. It's in the same league as tripping someone when they walk by - just dick behavior.

A prank is something the pranked can laugh at, not just the pranker.

Since I was just leaning to explore my sexuality during that time and my IM messages and emails reflected that I'd be pretty horrified to know someone stole my password, pwned my machine, and read them. Like, seriously horrified and very violated.

You call shaving cream on the hand a prank? VANILLA! (just kidding) Idk. I guess we were bad kids when I grew up because we would hack each other's runscape accounts and stuff and drop each other's stuff or transfer it to a fake account and hold for IRL ransom until somebody made you breakfast or something along those lines. Or we would watch somebody type their password on their laptop and if we caught it we would put a gross or lame picture on the desktop. I think if anything it actually built trust and friendship between us. Of course there was some drama once in awhile or you'd really make somebody mad, but at the end of the day we all stayed friends, and still are over a decade later. We had a lot of laughs, but it was like, ok who has the group not picked on recently? Time to prank them.

So while I understand in cases like yours it can be bad, I think calling for legal action and generally freaking out about it as a general rule is pretty lame. Kids will be kids. Shit happens. Life happens. Don't let people use your computer.