Please see the US-CERT (United States Computer Emergency Readiness Team, part of the Department of Homeland Security) Warning Regarding Apple QuickTime for Windows:

https://www.us-cert.gov/ncas/alerts/TA16-105A

As I read it, if your machine is running "Microsoft Windows with Apple QuickTime installed" it is "vulnerable to exploitation" and "The only mitigation available is to uninstall QuickTime for Windows".

The document links to Apple's directions for uninstalling QuickTime: https://support.apple.com/en-us/HT205771.