WASHINGTON — The Postal Service on Monday became the latest government agency to announce a major theft of data from its computer systems, telling its roughly 800,000 employees and retirees that an attack “potentially compromised” databases containing postal employees’ names, birth dates, addresses and Social Security numbers.

The announcement came just weeks after the White House disclosed an intrusion into its unclassified computer systems, which resulted in a shutdown of some of its communications while the malicious software was being removed.

The working assumption at the White House was that its troubles were caused by Russian hackers; the Postal Service attack, by contrast, seemed to have the signature of Chinese hackers. But attributing attacks is difficult, and first indications are frequently inaccurate.

“It’s an unfortunate fact of life these days that every organization connected to the Internet is a constant target for cyberintrusion activity,” Patrick R. Donahoe, the postmaster general, said in a written statement. “The United States Postal Service is no different. Fortunately, we have seen no evidence of malicious use of the compromised data.”