The malicious software—which was discovered two weeks ago by the U.S. Department of Defense’s Host-Based Security System—has been logging pilots’ keystrokes as their UAV’s fly missions over Iraq and Afghanistan, the report claims.

Worryingly, the malicious software has successfully resisted several attempts at deletion, according to unnamed sources in the Wired report, one of whom commented: “We keep wiping it off, and it keeps coming back. We think it’s benign. But we just don’t know.”

While military operations have continued and there is no evidence of classified military information being intercepted, authorities at Creech Air Force Base in Nevada—from which UAV operations in Afghanistan, Iraq, and other hotspots are mounted—will be worried about the potential implications of a security breach of this magnitude.