It has been discovered recently that the popular web-based jailbreaking tool for iDevices utilizes a PDF exploit to gain root access to the iOS software.
Apple was able to patch it so fast with iOS 4.0.2 for iPhone and iPod Touch, and iOS 3.2.2 for iPad. These updates will ensure that iOS platform remains secure.
iOS 4.0.2 is available for iPhone 3G and later running iOS 2.0 through iOS 4.0.1, and iPod Touch 2G and later running iOS 2.1 through iOS 4.0. iOS 3.2.2 is available for iPad running iOS 3.2 and 3.2.1.
Note that installing these updates will “un-jailbreak” your iDevice. However, your iOS will be more secured. The update is quite huge- 580MB for iPhone and 457MB for iPad; both can be downloaded via iTunes.