A flaw in some mobile phones based on Google's Android operating system makes it easy to bypass the phone's screen-lock facility.
Anyone who has the phone's number and access to the phone can bypass the screen lock to access any information stored on the device, according to US reports.
Attackers would simply have to call the targeted phone and then use the "back" button to go to the "home" screen, effectively bypassing the screen lock.
In the case of more advanced users, this could include e-mail messages and financial information such as personal identification numbers.
The flaw has so far been reported only in version 2.0.1 of Google's Android operating system used in Motorola's Droid phones.
Google has issued a limited response to the reports without providing any details about the problem or the steps being taken to fix it.
"We are aware of the issue and we are working to deliver a fix to Motorola Droids shortly," a Google spokesperson said.
Google recently-unveiled- Nexus One smartphone uses version 2.1 of the Android software.
Cybercriminals are likely to target both Android and Apple's iPhone operating systems in 2010, according to researchers at security firm Kaspersky Lab.
The first malicious programs for these mobile platforms appeared in 2009, which is a sure sign that they have aroused the interest of cybercriminals, they said.