UnitedHealth Group has responded to the "Biggest cybersecurity attack" on its subsidiary, Change Healthcare, by advancing more than $2 billion to healthcare providers affected by the disruption. The attack, described as one of the worst on the U.S. healthcare system, halted medical payments and created administrative challenges for providers nationwide, affecting vulnerable populations and disrupting services for three weeks. UnitedHealth Group CEO Andrew Witty reported progress in restoring impacted services. The U.S. government has launched an investigation into the incident, which has led to class-action lawsuits from healthcare providers over financial losses. The attack, occurring on February 21, has been under scrutiny for potentially breaching protected health data and causing a cash crunch for small healthcare providers.