Old PCs picked off rubbish tips can still hold data worth up to £85,000 to fraudsters.

Even deleting files from your hard drive can leave you open to identity theft, warns consumer watchdog Which?, as criminals can use free software to recover lost data.

There have even been reports of criminals trawling council tips and internet auction sites for PCs.

“It sounds extreme, but the only way to be 100 per cent safe is to smash your hard drive into smithereens,” warned Sarah Kidner, editor of Which? Computing.

“PCs contain more valuable personal information than ever as people increasingly shop online, use social networking sites and take digital photos. Even if you delete your files, you’d be surprised how easy it is to recover your personal data.

“Such information could bring identity thieves a hefty payday.”

Research by Which? Computing on old PCs bought from eBay found some people had not even tried to delete data, and one hard drive that initially appeared empty – after data was recovered – held 22,000 files.

The advice for people getting rid of an old PC is to use specialist deletion software.

Tests by Which? found these programs – such as McAfee’s The Shredder in its Internet Security Suite, TuneUp, DPWipe – to be effective at ridding a computer of data.

While using a new PC it is also worth considering if you do need to save some data. If sensitive data need be stored, PC users are advised to encrypt the data.

The final failsafe way to destroy data is to remove and destroy the hard drive.