Hackers could take control of an iPhone if its owner visits a doctored Web site or Internet hotspot, security researchers reported Monday.

The vulnerability of the vaunted device, Apple Inc.’s first cell phone, is only theoretical for now. There are no reports of criminals actually taking advantage of the security glitch to remotely access an iPhone.

But if it were exploited, hijacked iPhones could be very useful to the same gangs that take over personal computers and use them to disseminate spam, said Charlie Miller, principal security analyst at Independent Security Evaluators, which discovered the flaw.