Pharmacies across the United States are reporting that they are having difficulty getting prescriptions to patients because of a cyberattack on a unit of UnitedHealth. The company said in a regulatory filing Thursday its Change Healthcare business, which processes prescriptions to insurance for tens of thousands of pharmacies nationwide, was compromised by hackers who gained access to some of its systems. The company became aware of the cyberattack Wednesday, and, in a separate statement, said it expected the attack to last at least throughout the day Thursday. The cyberattack prevented some pharmacies from processing prescriptions to insurance companies to receive...