The purpose of VeriFast is to verify an entire proxy list with maximum speed - three proxies per second on average. Computer "threads" are small programming modules which execute nearly simultaneously, in parallel. Each thread will check one proxy from the list, then take the next until all proxies are checked.  You can define the number of threads in box Threads. The minimum is 9, maximum is 99.  More is not always better, it depends on your computer speed and other programs running at the moment.  
Press button Start to begin. The bottom status line will inform you how verification is progressing.  You can hit button Cancel at any time to stop the process. Clicking button Exit will bring you back to Hiproxy's Main Window.

Only HTTP proxies are verified, Socks are ignored.  Lite Edition will check only for access and ping response, Pro Edition will check access, ping, HTTPS and tunnel capabilities.  Verification settings (file, ping, https and tunnel) are defined in Hiproxy Settings.
Pro Edition users can browse and select a proxy list file different than the default defined in Settings.
The program requires Microsoft .NET Framework 1.1 installed, otherwise an error message will pop up.