A total of 143 million Americans could be affected by the incident.
Equifax recommends that individuals closely monitor their financial accounts and credit scores for unauthorized activity. "While we've made significant investments in cyber security we have more to do, and we will".
Equifax said the breach, which began in May, was discovered in late July.
Based in Atlanta, Equifax is a tempting target to hackers.
"In addition, credit card numbers for approximately 209,000 US consumers, and certain dispute documents with personal identifying information for approximately 182,000 USA consumers were accessed", read a statement from Equifax. Both Iowa and IL are among the 35 states that offer credit freezes, with each state charging $10 for the service.
A person's Social Security number is one of the primary ways identity is confirmed across the United States.