Secure your iDevices with PDF patch from Cydia.
Saurik, the creator of Cydia has created an actual patch which will completely close the hole (that was actually used to install the jailbreak) on all iOS based devices, including the first-gen iPhone and iPod touch which were left out in cold by Apple, making you completely safe running jailbroken iOS 4.0.1 / iOS 3.2.1.
It is available right now by the name of “PDF Patch” in Cydia. Install if before someone else exploits your iPhone.
Again, do NOT upgrade to the latest iOS 4.0.2 released by Apple, yesterday. If you do so, your Jailbreak and Unlock will be lost.