Exchange 2016 and 2019 servers were affected on New Year's Day. Microsoft was trying to store version date checks for its antivirus scanning engine in a 32-bit integer variable. Any date from January 1st, 2022 onward was too large and caused the engine to crash. The emergency fix uses a script to pause two services, replace the older antivirus engine files with newer ones that use a new number sequence, and restart operations.