In another attempt to stop hackers from accessing the PlayStation Network, Sony has put in place steps to shut down two widely-used methods in which hackers were able to play copied games on their console, online. Now, PSN will only accept consoles that are using the latest firmware (version 3.56). Hackers and pirates who use lower firmware version, which have been modified, will not be able to access PSN.
The first hacking method involved changing the DNS settings. It would redirect PSN to a web server which contained a file and this reported that the system was using the current firmware. The other method is pretty much the same as the first, but instead of a web server, hackers were using a PC to retrieve their information.
Usually, Sony employs this trick when they're close to releasing a firmware update, so this suggests that 3.57 might be released shortly. However, there is also a chance that this is now a permanent measure. Hopefully it will put an end to the vulnerability of the PS3.
Source: Edge Online