Sony's Efforts to Plug PSP Holes Although homebrew programs and games technically aren't illegal, provided that they don't contain copyrighted material, Sony doesn't want the PSP to run them. By default, the PSP checks for a digital signature from Sony before it runs software; homebrew basically is unsigned software. Sony has been mostly silent about homebrew. The company did issue a statement, however, when a PSP virus (named Trojan.PSPBrick by Symantec) got loose in the wild, because that virus would be executed only by people trying to downgrade their PSP firmware to run homebrew. The statement read, in part: "Sony Computer Entertainment does not condone the activities of those who modify their PSP, as it can introduce unauthorised and potentially dangerous software code into the PSP and invalidate the warranty." Sony refused to offer warranty repair to PSP owners whose systems were damaged by the virus. Each revision of Sony's firmware has taken steps to plug the holes that allow homebrew software to be executed on the PSP: Version 1.00, the original PSP firmware, was cracked relatively quickly and easily. It could execute programs simply dropped onto a Memory Stick Duo. In addition, a homebrew app allowed users to save their 1.00 firmware to a Memory Stick Duo (which would be unique to their own PSPs); if users upgraded to the next firmware version (1.50), they could downgrade back to 1.00. Version 1.50 could run homebrew in two ways: by swapping out a pair of Memory Stick Duos or by using a program called KXploit. The next major revision, version 2.00, offered an official Web browser as a value-added feature. An image-manipulation bug allowed homebrew to be run, and someone found a way to downgrade this firmware revision to version 1.50 for even better homebrew compatibility. Versions 2.01 to 2.60 could run homebrew by installing an eboot loader, or eloader (a special homebrew program loader), as a save-game file for Grand Theft Auto: Liberty City Stories (Figure 12.5). Figure 12.5. An excellent game, GTA: Liberty City Stories is also a homebrew tool. 
Versions 2.70 and 2.71 (the current version at this writing) have yet to be cracked. Of course, it's only a matter of time....
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