I've had one report where stupid Norton was blocking the Sigil 2.0.2 installation because the installer was trying to delete files from Sigil's own program directory. The Sigil installer has ALWAYS done that. And why would it be a problem in an in-place update/install?
The InstallDelete functionality of InnoSetup is standard, and Sigil has used it to create its Windows installers for years and years.
Just further proof (for me) that third-party Windows antivirus programs are a waste of time, money, and resources. They cause more problems than they prevent.