Make sure Adobe and your java is updated and the older versions removed.
Adobe don't update just 1 part of it. Update the whole suite. Flash, pdf reader writer etc etc.
If you got a lot of pcs think about a hardware firewall. Have the logs monitored for a month or two and use the data to set up strong rules. Security ain't fire and forget. It needs some to look over it on a regular basis.
Microsoft releases patches every tuesday. Set your updates for Tuesday 5pm or around that time.
Use a strong password to lock up the admin account.
Disable the guest accounts and all unused accounts.
Use a offline scanner from a cold boot to scan all the computers.
Make use of gpo to set restrictions over the network.
Remember your worst enemy ain't infected sites on the internet or some exploit. Its the users inside it normally doing idiotic and stupid things.
Also the harder your trying to block things the more extreme measures their going to use to bypass it.
Blocking like piratebay won't get you much anywhere as you can search from with a torrent program.
P2P protocol is not illegal its the users actions over it thats wrong. One thing clearly wrong in this world as some stupid isps shows trying to do all things to P2P traffic. But a lot of games use the same protocol and its traffic look the same as the torrents will. Then encryption all bets are off.
Get a decent antivirus product. Decent I mean a enterprise suite and get some sort of hardware firewall.