[TeMPOraL]

Or 7) someone who did it for teh lulz. While rare, this also happens. But I agree; it's hard to guess motivations behind the attack without more info.

[brownbat]

8) Waterholing targeting a user or group that frequents the site?

I like #2 though, or as I'd put it: flotsam of the internet, like how slammer ended up at davis besse.