Tip #44: Blocking statistics by IP address and user-agent
Did you know that in OpenX 2.8, you can, when Working as the Administrator account, go to Configuration > Global Settings > Banner Logging Settings, and in the Block Banner Logging Settings section, specify a list of IP addresses and user-agents which you do not want to log any statistics from?
If you have a small list of known IP addresses and/or user-agents that are causing invalid spikes in your statistics that you would like to block, then this is the place to do it.
Alternatively, if you are a relatively large publisher, you can use the IAB Spiders & Bots list here.