The scam might be an email with the logo, letterhead and mailing address of a well-known company, or hospital. If you click on a link in their email, the hackers will infect your computer with malware, like Cryptolocker.
They'll take over your computer, and often threaten to blackmail you, unless you pay them ransom. Then you have to decide how much your files, whether they're irreplaceable photos or your business records, are worth.
In fact, take a second and really think about how much you'd be willing to pay to get your files back. That's how much you should be willing to pay for an Internet security suite that keeps ransomware hackers out of your devices, so your ID, financial information and medical records are safe.