Plenty of software engineers post and lurk here, so they can offer their input.
On the consumer side, you have probably installed software on your PC. The Windows OS has an "uninstall" program that is supposed to remove traces of the installed program. Maybe something like this was used.
“...an “uninstall” program that is supposed to remove traces of the installed program....”
An auto/self-executing “uninstall” program. How sweet, convenient and untraceable could that be? I’m thinking almost anything’s possible. We’ll never know for sure.