The fake websites were meant to mimic the web pages of services provided by the Federal Reserve Bank of St. Louis, including Federal Reserve Economic Data, or Fred, a database of economic data culled from over 70 sources, and the Federal Reserve Archival System for Economic Research, which includes historical data. The hackers also mimicked the bank’s data mapping service and a service that allows users to look at vintage displays of economic data.

“As is common with these kinds of D.N.S. attacks, users who were redirected to one of these phony websites may have been unknowingly exposed to vulnerabilities that the hackers may have put there, such as phishing, malware and access to user names and passwords,” the agency said in a statement.

The agency said the website of the St. Louis Fed had not been affected. The attack was first reported by Krebs on Security, a blog popular with security experts.

A spokeswoman for the Federal Reserve Bank of St. Louis said that she did not yet know who was behind the attacks. The Federal Reserve had no comment about the attack.

Security experts say that domain name system attacks require significantly more skill than a typical website attack. By attacking the domain name registrar used by the St. Louis Fed, it is possible that attackers may have been able to compromise the security for some or all of the sites that rely on the security of the domain name registrar.