From The Apple Wiki

The iPhone Elite Dev Team Virginizer is a tool designed to repair the changes that AnySIM 1.0.x and others (including iUnlock and hardware unlocks) did. When 1.0.2 was unlocked, the seczone became corrupted, causing a brick when upgraded to 1.1.1. The virginizer reflashed the 1.0.2 baseband and repaired the seczone. Because of this, your phone will be relocked, allowing a safe update to 1.1.1 and unlock with AnySIM 1.1.

It doesn't work for IPSF, unless you have a full NOR dump.

There was never actual corruption, rather the sectable was rewritten to have an unlocked state, while the encrypted token remained untouched. When flashed with an unpatched firmware, the unpatched firmware read the sectable and token, saw a mismatch and booted into XSIMSTATE mode 2, meaning invalid crypto. This caused the baseband to appear bricked.