Warning as second-hand phones used to steal old owner's data

A warning to anyone who has sold their old smartphone to a stranger, with thieves using erased devices to recover photos, emails and financial records.

9NEWS purchased five second-hand phones on Gumtree and took them to a data recovery centre.

More than 19,000 files were retrieved from just two of the phones, including photos, videos, documents and emails.

Private information that sellers thought were gone forever were recovered within 48 hours.

Data recovery specialist Daniel Etezadi from Century ID said performing a factory reset will not delete the data.

"When it comes to recovery, we can recover all of it," he said.

Lawyer Simon Creek told 9NEWS there is little the law can do to help.

"If you hand over your phone, your laptop, your tablet, any data on there becomes the property of the new owner," he said.

Data recovery experts said you can safely sell a used phone by formatting the hard drive and uploading random data to it, however it is time consuming and can be difficult.

Failure to do so could so could allow criminals to steal your identity of use the information for extortion.

Their advice was to pull out the hardware from any laptops and computers before selling them. For mobile phones, you are better off keeping them as a spare.

Watch the video in the player above to see the full report.