blackice

Another easy & free thing you can use is proxy detection, sites like https://getipintel.net would beneficial in preventing fraud.

There are many traffic exchange sites that use automated software to click or view ads. Most of them run on server ips or they're using a proxy. http://getIPIntel.net is a free and useful service to combat bad / low quality traffic. Though to save you money, your advertiser needs to not bill you for automated traffic. It's unlikely that'll happen because the more views and clicks, the more money they'll get. You can still use GetIPIntel's api to help you pick which advertising company gives you legitimate traffic.

The slides mention IP reputation and a great free resource for that is http://GetIPIntel.net to make sure unexpected IPs don't connect to your services.