I just found this out a few days ago.

ClickBank has sophisticated IP filters in place that prohibit people from hitting their website and their order forms too quickly.

If ClickBank detects too many requests in a short period of time from a single IP, then that IP is blacklisted until the flooding stops.

See the screen-shot below:

The IP will be opened again once traffic stops from that IP for around 2-5 minutes.

What does this mean for you? It means more robust/secure ordering system as this filter should be able to filter out all the spam-bots.