Strange issue we saw this week involving our physical Win 10 1909/20H2 clients. We had gotten a few calls that users couldn't launch Teams on their workstations. The error was "application was unable to start correctly (0x0000364)" We found that the ffmpeg.dll file in C:\Users\username\AppData\Local\Microsoft\Teams\current was being blocked. We use Applocker so we thought maybe the signing certificate changed and wasn't whitelisted. However when we viewed the digital signatures on the file, we saw "The digital signature is not valid/The digital signature of the object did not verify." The file is signed by the Microsoft CAs, and we can't find anything wrong with the certificate chain or revocation checks. Running Get-AuthenticodeSignature results in a status of HashMismatch. Has anybody seen anything like this? Aside from some malicious process altering the file hash, is there any other reason for a hash to get altered? We're going to take it up with our AV vendor to see if they have any idea. We're not seeing any findings by running AV scans against the affected systems, and we uploaded the ffmpeg file itself to virustotal which came back clean.