Although the main reason for the recent 3.21 Firmware update was to remove the OtherOS option from the older PS3 models, the firmware also contains a few undocumented features (undocumented in North America and Europe). The Japanese version of the Firmware 3.21 changelog mentions two new features included in the firmware.
The two new features include improved quality of PlayStation Network titles and vulnerabilities fixes for MP4 playback on the system. Does this mean that another exploit was present in the system?
Japanese Website Changelog:
* PlayStation®Store ??????????????PlayStation®?????????????????????????
* MP4???????????????????????????????
Rough Translation:
* PlayStation ® Store in part can be downloaded from PlayStation ® format software has improved the quality of work.
* Added support for security vulnerabilities for MP4 video files for playback.