It is still a served ball, and should be treated the same as the one that cleared the net.
you still have to return it as a serve, so no you can not attack it.
I think the idea of being able to attack the serve because it hit the net is another one of those word of mouth rules. I looked through the book and I can not find anything in the book to back up that idea.
It depends on the rules your playing by. Rally score you play it normal, so no attacking, but its playable. Side out scoring, its a side out. Your own rules and scoring… priceless.