More than 70,000 AT&T users reported that their cell service was down Thursday morning—part of a massive outage that prevented police from receiving some 911 calls, the New York Post reported. Downdetector, which allows users to self-report outages from cellular carriers and websites, showed that outages peaked around 8:10 a.m. with 74,000 AT&T users reporting they had no service. By comparison, 26 people reported having an outage at 10 p.m. Wednesday. The outage also appeared to affect T-Mobile, Verizon, Boost Mobile, Consumer Cellular, and Straight Talk Wireless customers, the Post reported, but on a smaller scale. Federal sources told ABC News the outage is being probed as a potential cyber attack or hack, though it also could have been a technical malfunction. By late Thursday morning, the carrier said it had restored 75 percent of its network. The outage reportedly affected users in New York, Boston, and Atlanta, as well as some in Houston, Dallas, Los Angeles, Seattle, and San Francisco.