The service is free of charge if you place a backlink. Otherwise it will cost $40/mo. The idea of this API is similar to spamcop´s but it´s against open proxies that are also being used to send mass spam emails in case those proxies allow SMTP port 25. Sort version of it´s advantages: Around 75% of all open proxies (anonymous or transparent) will get defeated by the NiX API that are being used to abuse your sites/services. For example my internal investigation proved that nearly all of the open proxies are being used to abuse CPM or other ADS releated services to make the clicks through the proxies and so on ...the list is very long Question: How the proxies are being tested and based on what decision it will be blocked? Answer: Proxies are being crawled and tested fully automatically using private tools such NiX Proxy Checker PRO 1.5.3 for Linux and NiX Forum Proxy Leecher 1.0.1 for Linux (it can crawl 100 000+ listed proxies from the forums and other sites in less than five minutes) and the crawled list is constantly being updated. Just a small example: |NiX| Checked 42724 proxies in 2 hours 46 minutes 25 seconds. Threads used: 100 Working proxies: 1427. That speed is from P4 3GHz machine using only one instance of NiX. Proxies are tested against real web site to determine they're fully working and are open. This check covers all common proxy types, http, ssl, socks 4 and 5 Learn More