While their primary use remains to make telephone calls, cell phones have come a long way. Thanks to their growing computing power and complexity, cell phones have become mini computers.

"As cell phones have gotten more computational power, it's been feasible for people to do the same with them as people did with PCs," said Dave Farber, a distinguished professor of computer science at Carnegie Mellon University.

Consequently, cell phones are starting to acquire some of the same problems that for years have plagued PC users, including viruses and the threat of identity theft.

A number of security companies that provide antivirus software for computers -- Symantec, McAfee and Sophos -- recently have created similar products for mobile phones.

Three years ago, people who downloaded ring tones and screen savers for their cell phone from several Web sites found that every icon on their cell phone screens turned into a skull-and-crossbones. The virus further disabled their phones so they couldn't send or receive text messages or access contact lists or calendars.

"We haven't seen it become a huge issue yet, but we'll see it grow significantly over the next several years," said Todd Davis, chief executive of LifeLock, an anti-identify theft company in Tempe, Ariz.

"What you have now are really smart guys trying to show off what they can do to outsmart the system," Mr. Davis said. "Eventually they will figure how they can turn it into money."

Personal computers may provide a glimpse of the future for cell phones. But Anand Raghunathan, a senior research staff member at NEC Laboratories America in Princeton, N.J., said for now there is little threat of a large scale cell phone virus.

Whereas Windows is the dominant operating system for PCs, "cell phones are more fragmented in terms of operating systems and applications," Mr. Raghunathan said. "The fragmentation makes it more difficult for viruses to spread large scale.

"There have been very few viruses that could affect cell phones across different operating systems and applications."

But because they are more easily lost or stolen than personal computers, cell phones have their own unique set of dangers.

People are using their phones to connect to their company's network to view e-mail or download and read confidential company documents. They use phones to trade stocks, read bank statements and transfer money between bank accounts.

All of those things increases the critical need for protecting a cell phone's contents.

"One of the biggest holes from a vulnerability standpoint is Bluetooth technology," Mr. Davis said. "Anyone with another Bluetooth device can engage our cell phone and we'll never know it.

"If they want to pull data, you'll never know it -- contacts, calendars, notes, passwords. Anything that can be stored on cell phones can be retrieved using the Bluetooth because what you've done is allowed someone to log onto your cell phone."

Data stored on cell phones can be protected, but users have to be technically savvy to do so, he said. And the anti-spyware that is available for cell phones tends to drain their batteries faster and make the phones themselves less useful.

"It's just beginning. It's not a major problem now," said Dr. Farber. "But over the next few years as cell phones become more elaborate, people will start thinking they are attractive to attack."