WASHINGTON (AP) — U.S. authorities are expressing increased alarm about an intrusion into computer systems around the globe that officials suspect was carried out by Russia. The cybersecurity unit of the Department of Homeland Security said Thursday the hack “poses a grave risk” to the federal government and state, local, tribal, and territorial governments as well as critical infrastructure entities and other private sector organizations. It was the most detailed comment yet from the Cybersecurity and Infrastructure Agency since reports emerged that government agencies including the Treasury and Commerce departments were among those penetrated. CISA also warned that it will be difficult to remove the malware inserted through network software.