Actually, they're both bad.
The first one doesn't show character information, and it's not clear that he's the one vaccing because there are two other people on the map, and one of them being named 'sadasaas' raises more suspicion to him.
The second screen shot shows the mob being hit by a character outside of the screen with Slash Blast.
I would say that the first screen shot is the better of the two because, although it doesn't show character information, it shows the person attacking a mob of vacced monsters. It's still sketchy though.
But yes, I agree that Assassins are a very poor choice to hack with. They're idiots. I've seen Hermits vaccing with Lucky Sevens.
So what should I do? Unless you can put up two screenshots, there'd be no way to verify the character information.