Hacker Charlie Miller, who just discovered an SMS vulnerability that affects the iPhone, suggests that it is very unsafe to use a jailbroken iPhone. Jailbreaking is when a user removes Apple's barriers to installing third-party applications, allowing users to install software that is not distributed via the iTunes Store, as well as cracked software. It also allows users to use the iPhone with carriers other than the exclusive carrier in their country. (iPhones without carrier limitations are sold in a handful of countries, but currently not in the US, for example.)
At the SyScan security conference in Singapore, Miller said, "If you care about security, don't use a jailbroken iPhone." He said that jailbreaking removes about 80 percent of the security protections built into the iPhone software, leaving users open to a wide variety of attacks.