Alas - Shakespeare didn't know the half of it!
I also read about this elsewhere and my reaction was the same:
Excuse me ?? I fail to see the ethical breach here. I suppose if you had a home security system (ADT, et al) and it went out hunting for miscreants, it would be 'vigilante justice'.
On the other hand - there is no guard system, guard dog, police force, viable law - protecting us from spam. The people who flood my mailbox with offers for Rolex, Viagra etc., penis enlargement, lottery winnings (lottery enlargement and penis winnings - whatever) - and those who send the charming messages that have graphic sexual phrases - in the subject line - for God's sake (what does that mean, Mommy) - don't deserve 'vigilante justice'. They deserve to be hanged, drawn & quartered!