The exploit used by Comex to run the jailbreak through Safari is as simple as ingenious. The code must be injected via a. PDF and executed by the system. This does present significant risks to sensitive data on your device, as long as the port used dall'exploit remains open us to any attacker might install malicious packages.
Use the Guide at
http://www.spiritjb.org/2010/08/important-how-to-fix-serious-security.html