DDoSing all pools would require even more lots of (expensive) botnet members. I'm not sure if this pays off.
Cost to prevent bitcoin mining < Cost to mine bitcoins
Expensive botnet members?
I can buy 1000 bots for 100$ or less, and have em DDoS for me.
Even cheaper if I write my own bot, which is not very difficult (even a FUD one).
If a botnet owner w/ around 15000 zombies (not very uncommon) wanted to mine coins, by golly he could. Set 7500 of em to CPU mining, the other 7500 to DDoS'ing the pools with bad packets.