SAN DIEGO -- Today's criminal has a number of weapons at his disposal, but you might be surprised to learn one of their cheapest and most effective tools is a cell phone.

The tools of choice for today's savvy criminals are prepaid cell phones. They're cheap, disposable and totally untraceable.

The problem is law enforcement officials working undercover have no way of knowing who they're dealing with when criminals use these phones.

And it's not just criminals using these phones.

Within the last year, terror suspects were arrested in Ohio, West Virginia, Texas and Michigan buying hundreds of prepaid cell phones at one time.

"Our biggest concern is that the criminals are making a lot of money very quickly and unreported, which could in turn fund a terrorist organization," said FBI public affairs specialist April Langwell.

10News conducted its own undercover investigation and found most stores will place a limit on prepaid cell phone purchases.

But one store helped a 10News producer and photographer overcome the problem by allowing them to buy two cell phones each, and there wasn't a concern about identification.

The appeal of prepaid cell phones to criminals and terrorists has become such a concern, several states are proposing laws that would force consumers to provide identification when buying prepaid cell phones. It's legislation that has the wireless industry concerned.

"I don't think anyone argues about it being a well-intentioned initiative, but we're concerned that in practice, that it just might not work the way people think it would work," said Joe Farren, with the CTIA-Wireless Association.

10News asked California assemblymember Joel Anderson his thoughts about the prepaid cell phone issue and if legislation would be considered here.

"I think this threat is very credible. In fact, as a member of public safety, I drafted this letter today and we're going to be mailing it off to the Public Utilities Commission to look at this issue in-depth," said Anderson.