Apple announces iOS 4.0.2, to fix PDF exploit discovered by Comex. This patch is available for the following iDevices

• iPhone 4
• iPhone 3GS
• iPod Touch 2G/3G
• iPad (OS 3.2.2)

If you own any other iDevice, Apple is probably not putting any efforts to make your device safer from this vulnerability.
If you want to make your iDevice safer, jail breaking could be the only way for such devices. Saurik, the creator of Cydia, has patched all the iDevice from this exploit. You must apply this patch after using jailbreakme.

Patch is available in cydia by the name “PDF Patch”. Open up cydia in your iDevice, and install this patch as you install any other software in Cydia.