Phorm Check API
Phormcheck is an interesting third party solution, analogous to the DNS system.
It comprises a database of ISP address ranges.
An API is provided allowing you to perform a database lookup, to determine whether a given user originates from a Phormed Internet Service Provider.
The site provides sample client code for the API, and other useful countermeasures... such as a dynamic robots.txt, a warning banner function, and techniques for detecting cookie interference.
Benefits of a database driven approach include the accuracy of the lookup; you don't have to maintain local copies of an htaccess block file, or maintain a blocking script.
However, to maintain optimum scalability and performance you should use the caching client API, or optimise the calls to reduce frequency of lookups.
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