Hackers buy and sell breached data in order to impersonate people or carry out scams. Here's how you can find out if your data has been leaked online and protect yourself. More records are stored online than ever — and it's becoming increasingly common for large swaths of personal data to fall into the hands of cybercriminals. Over 4 billion records have been stolen or accidentally leaked in the past decade, according to data collected by Privacy Rights Clearinghouse, with more than 7,000 separate breaches in that time, and the frequency of mega-breaches that compromise tens or hundreds of millions of people's data is on the rise.