Where we get proxies?

We collect proxies from open sources around the internet. Our "spider-robot" has a large database of different websites, including forums where proxy servers are published. When visiting such websites, the robot finds references similar to proxies, for example, a 1.2.3.4:8080 format, and takes them for verification by a proxy checker. If the check gives a positive result, the proxy gets into our proxy list. Later, proxies are regularly checked and if they stop working, they are automatically deleted from the list.