People who are planning to sell their mobile phone have been encouraged to make sure that all the information stored on the device has been deleted.
According to research by Good Mobile Phones, more than two-thirds of people who sold on their handset did not clear the personal data it contained beforehand.
This, it stated, means they could be vulnerable to identity thieves, as text messages and photographs could contain highly sensitive information, Computer Weekly reports.
Good Mobile Phones noted that those who have sold internet-enabled phones could be especially vulnerable, particularly if their browser history has not been erased.
The organisation said this is because the handset could still contain log-in information for various websites regularly accessed by the previous owner.
Mark Owen, managing director of Good Mobile Phones, commented: "Always ensure that all stored information is wiped before selling a mobile on.
"At the very least, you don't want anyone flicking through your personal pics."
Good Mobile Phones noted that pictures accounted for more than half of the personal data that had not been erased.
Figures also showed that people frequently leave contact details stored on their handset, as well as videos.
One in three people who had left data on their handset were found to have done so because they were unaware that it would be saved on the device.
Meanwhile, 43 per cent of those polled said they forgot to remove the personal information when they sold their phone.
This comes after research by Lloyds TSB revealed that one in three mobile phone owners use their handset as a calendar.
The study also found that nearly one in five people regularly check emails on their device, while more than half use the alarm clock function.
Lloyds TSB said this shows that mobile phones have become a "one stop shop" for millions of people that they cannot live without.