The US Department of Justice (DoJ) has been sending phishing emails to its own employees to test their security awareness.

DoJ staff have been receiving emails from the 'Thrift Savings Plan Account Coordinator' over the past two weeks, asking them to enter their log-in details by 31 January to get information about their 401k savings plans.

However, many employees recognised that it was a phishing email and began filling up inboxes with warnings about the bogus message. The DoJ has now admitted that it was a test.

"We have learned that the messages are part of a hoax invented and distributed by the DoJ to test employee security awareness," said a memo circulated by Ted Shelkey, assistant director for information systems security at the DoJ.

"The [emails] are not malicious, and there is no need to distribute warning messages to colleagues and law enforcement contacts. Please delete all such messages and associated alerts."

DoJ spokeswoman Gina Talamona told Associated Press that the emails were a security test. "This specific exercise was successfully completed within the defined time period," she said.

"Scenarios are intended to represent an example of persistent cyber threats facing today's internet users."