Equifax says a giant cybersecurity breach compromised the personal information of as many as 143 million Americans — almost half the country.

Cyber criminals have accessed sensitive information -- including names, social security numbers, birth dates, addresses, and the numbers of some driver's licenses.

Additionally, Equifax said that credit card numbers for about 209,000 U.S. customers were exposed, as was "personal identifying information" on roughly 182,000 U.S. customers involved in credit report disputes. Residents in the U.K. and Canada were also impacted.

The breach occurred between mid-May and July, Equifax said. The company said it discovered the hack on July 29.

The data breach is one of the worst ever, by its reach and by the kind of information exposed to the public.

Related: The biggest data breaches ever

"This is clearly a disappointing event for our company, and one that strikes at the heart of who we are and what we do," said Equifax chairman and CEO Richard F. Smith.

Equifax is one of three nationwide credit-reporting companies that track and rates the financial history of U.S. consumers. The companies are supplied with data about loans, loan payments and credit cards, as well as information on everything from child support payments, credit limits, missed rent and utilities payments, addresses and employer history, which all factor into credit scores.

Related: How to find out if you're affected by the Equifax hack

Unlike other data breaches, not all of the people affected by the Equifax breach may be aware that they're customers of the company. Equifax gets its data from credit card companies, banks, retailers, and lenders who report on the credit activity of individuals to credit reporting agencies, as well as by purchasing public records.

Equifax is mailing notices to people whose credit cards or dispute documents were affected.

Related: Instagram hackers are selling user emails and phone numbers

It also says that consumers can check to see if they've potentially been impacted by submitting their name and the last six digits of their social security number. Users are given a date when they will be enrolled in free identity theft protection and credit file monitoring services. Equifax did not immediately reply to CNN Tech's request for more information about the process.

"This is reason Number 10,000 to check your online bank statements and credit card statements on a regular basis, ideally weekly," said Matt Schulz, senior industry analyst at CreditCards.com. "Bad guys can be very patient, so it's important to keep an eye out long after this story fades from the headlines."