Microsoft OneDrive for Business modifies files as it syncs.
“To check if OneDrive for Business was the culprit, I created a handful of mostly empty files of different types I frequently use and handwrote a simple PHP file and HTML file in Notepad++, so any modifications would clearly stand out. I then used MD5summer to create MD5 hashes and then placed these files in a folder for OneDrive for Business to sync. A few hours later, I booted my laptop which also has OneDrive for Business installed and a moment later, this folder appeared. I then ran MD5summer and this is what I got:”