The United States Postal Service is the latest victim of a wide-scale online data breach.
A USPS spokesman told NPR today that more than 800,000 employees may have been affected. In a statement, USPS said "names, dates of birth, Social Security numbers, addresses, beginning and end dates of employment, emergency contact information" may have been compromised.
USPS says customers were affected as well. Although the service couldn't provide an exact number, it did say customers who contacted their Postal Customer Care Center via phone or email between Jan. 1, 2014, and Aug. 15, 2014, might be vulnerable.
The FBI is leading an investigation into the hack, and USPS said all of its operations are still functioning normally.
It's unclear who might be responsible for the hack, though The Washington Post writes that "some analysts say that targeting a federal agency such as the post office makes sense for China as an espionage tool." NPR previously covered allegations that Chinese hackers accessed U.S. government computer networks earlier this year, to find information about employees who have applied for top-secret security clearances.
USPS says it's offering a year of free credit monitoring to employees and customers who may be at risk. The organization also apologized for the breaches:
"The privacy and security of data entrusted to us is of the utmost importance. We have recently implemented additional security measures designed to improve the security of our information systems, including certain actions this past weekend that caused certain systems to be off-line. We know this caused inconvenience to some of our customers and partners, and we apologize for any disruption."
USA Today is reporting that USPS told members of Congress about the hack in two briefings over the past few weeks. Democratic House member Elijah Cummings of Maryland sent a letter to the postmaster general Monday, requesting more information on the breach and sounding the alarm on the recent frequency of these types of hacks.
"The increasing number of cyber-attacks in both the public and private sectors is unprecedented and poses a clear and present danger to our nation's security," he wrote.
So far this year, multiple large organizations have been victims of wide-scale data breaches, including Target, Home Depot and the federal contractor USIS.