From The Register:

Affiliates of terrorist organization Hezbollah cloned the mobiles of senior executives of Canadian operator Rogers Communications, including chief exec Ted Rogers. Even though the firm had technology in place to trigger alerts over suspicious departures in call activity, Rogers staffers were too frightened of inconveniencing bosses to do anything about the fraud, Canadian paper the Globe and Mail reports.

The scam only came to light after law professor Susan Drummond challenged a mobile phone of C$12,000 she received after her return from a month-long trip to Israel. The monster mobile bill listed more than 300 calls made in August to foreign countries including Libya, Pakistan, Russia and Syria. Drummond was told she'd have to foot the bill despite her protests than she'd never previously made overseas calls using the account. Her normal bill was around C$75.

Clone cell phones? How does this happen?

This is how the bad guys cloned phones

First, they used a scanner to record electronic serial numbers (ESNs) and Mobile Identification Numbers (MINs), or telephone numbers. Then they programmed their own mobile phones to transmit the ESN/MIN data to the cell phone network.

Most people would complain about a huge cell phone bill with multiple calls to unknown phone numbers, but the terrorist group counted on the Rogers staffers to be too afraid to say anything about the exec's irregular phone bill. This strategy worked... For a while at least.

Should you be worried?

The answer is no, for a few reasons. Cell phone service providers quickly implemented encryption technology on their networks to prevent scanners from picking up your ESN/MIN information. Even if someone did get it, and managed to program it into another device, it would be fairly obvious it wasn't you making the calls.

Here's why

When you make a phone call from your device, the information is transmitted to the nearest cell site. Your phone then "camps" on that cell site until it is "handed off" to the next cell site.

Let's say you have been making phone calls from Washington DC during one billing cycle. When you get your bill, you see that calls have been made from Toronto, Ontario during the same billing cycle.

Your phone company will then go through each disputed call, and compare it to other calls made around the same time. If you made six calls in the morning of December 17th from Washington, DC, and a phone call to Libya made from Ontario shows up on the bill within a few minutes of the ones made from Washington DC, your phone company will know something is wrong, and fix it.

Don't worry about it though, it's a non-issue. Most phone companies use complicated encryption technology, which renders this practice almost impossible.