There are a number of nefarious sites and services that allow you play a tricks on your friends by spoofing their cell phone—that is, texting or calling under the guise of another person. A new report by security researcher and iPhone jailbreaking expert, pod2g, discovered that the iPhone's messaging service posses a security flaw that makes it especially susceptible to such attacks. 

According to pod2G, the issue lies with the way iOS deals with User Data Header (UDH) info: 

"In the text payload, a section called UDH (User Data Header) is optional but defines lot of advanced features not all mobiles are compatible with. One of these options enables the user to change the reply address of the text. If the destination mobile is compatible with it, and if the receiver tries to answer to the text, he will not respond to the original number, but to the specified one.

"Most carriers don't check this part of the message, which means one can write whatever he wants in this section : a special number like 911, or the number of somebody else.

"In a good implementation of this feature, the receiver would see the original phone number and the reply-to one. On iPhone, when you see the message, it seems to come from the reply-to number, and you [lose] track of the origin." 

In order for someone to maliciously exploit this hole, the person would need to know the name and contact info of someone already in a person's phonebook. But once they do, pod2G says a hacker could use phishing attacks to get people to click links that would send them to harmful sites.  

[Pod2g via MacRumors]