Hackers breached computers belonging to the State Department, The New York Times reports, making it the fourth attack targeting government computers in recent weeks. While it’s not clear who attacked these targets and for what purpose, the State Department, the White House, the United States Postal Service and the National Oceanic and Atmospheric Administration have all reported similar breaches recently.

The State Department on Sunday became the fourth government agency to announce a breach of its computer systems in recent weeks, after an infiltration forced the agency to temporarily shut down its unclassified email system and public websites. The breach, which the agency said did not affect any of its classified systems, follows a similar one involving the unclassified computer systems of the White House last month, which also resulted in a temporary shutdown of its communications systems. There have been similar breaches at the United States Postal Service and the National Oceanic and Atmospheric Administration. It was not immediately clear if the attacks were related. The State Department breach was first reported Sunday by The Associated Press.