The biggest U.S. health insurer, Anthem Blue Cross, revealed Thursday that hackers obtained data on up to 80 million current and former customers. The compromised information includes Social Security numbers, email addresses and birthdates as well as such employee data as income.

Given the steady stream of data hacks – whether it’s Target, Home Depot or Anthem – how much is all this data worth?

Unlike previous high-profile hacks, the Anthem hackers did not take credit card numbers. But personal data, like Social Security numbers, can be even more valuable on the so-called “Dark Web,” the invisible part of the Internet you can’t find on Google.