Seventy per cent of formatted second hand laptops contain retrievable data.
Research from security firm Pointsec found they were able to retrieve data on 70 out of 100 hard-drives bought over the internet.
One hard-drive contained data on pension plans, payroll records and passwords for a European financial firm intranet site.
"Our research has found how easy it is to purchase second-hand or lost laptops and access the information on them," said Peter Larsson, CEO of Pointsec Mobile Technologies. "Even when companies or individuals believe they have wiped the hard drive clean, it is clear how easy it is to retrieve sensitive information from them."
Pointsec found 77 Microsoft Excel documents containing email addresses, dates of birth and other information, which if exposed could have damaged the unnamed company.
Researchers also found that police and travel authorities auctioned lost laptops after three months if unclaimed. The firm visited one of the auctions used by Gatwick airport, and found before buying, they were able to access data on one in three machines.