Android users take note: reformatting your old phone before selling it may not be enough to protect your sensitive personal data from the next person who uses the device.

Free data recovery apps can be used to access photos, videos, passwords and documents on old Android phones, even after they've been supposedly deleted, a CTV Vancouver investigation has found.

The problem stems from Android's old version 4 and version 5 operating systems, which do not include automatic encryption for users' sensitive information.

In a test orchestrated by CTV Vancouver, security experts at Fortinet Global attempted to recover data from more than a dozen old cell phones. The phones included both Android and iPhone devices, and were acquired from a variety of sources, including resellers, Craigslist and individual donations.

The security experts managed to recover vast quantities of information from some of the old Android phones, even after they had been repeatedly wiped through the settings menu.

"When you do a reset, the issue is that the operating system just unlinks the data. It's not physically wiping out all of the data," Derek Manky, a Fortinet security strategist, told CTV Vancouver.

Fortinet expert Douglas Santos says free apps can easily find old data if it is not encrypted. "It's scanning the blocks and looking for patterns of that data," he said.

"They're never truly deleted off the drive," Manky said.

Manky and Santos says the only way to guarantee the safety of your data before reselling a phone is to make sure it's encrypted first. That can be done in the device's security menu.

"They're not going to be able to get access to that encrypted data unless they know the pin code for it," Manky said.

All iOS devices and new Android devices encrypt their data automatically, but the feature must be enabled on older Androids.

Manky says it's an easy precaution to take, especially for anyone who plans to sell an old phone or hand it off to a friend.

"People have a false sense of security way too often," he said.

With files from CTV Vancouver