Here is post by US Homeland Security. Department of Homeland Security.
Systems Affected
Microsoft Windows with Apple QuickTime installed
Apple will no longer be providing security updates for QuickTime for Windows, leaving this software vulnerable to exploitation.
Description
All software products have a lifecycle. Apple will no longer be providing security updates for QuickTime
The Zero Day Initiative has issued advisories for two vulnerabilities found in QuickTime for Windows.
Impact
Computer systems running unsupported software are exposed to elevated cybersecurity dangers, such as increased risks of malicious attacks or electronic data loss. Exploitation of QuickTime for Windows vulnerabilities could allow remote attackers to take control of affected systems.
Solution
Computers running QuickTime for Windows will continue to work after support ends. However, using unsupported software will increase the risks from viruses and other security threats. Potential negative consequences include loss of confidentiality, integrity, or availability of your data, as well as damage to system resources or assets. The only mitigation available is to uninstall QuickTime for Windows. Users can find instructions for uninstalling QuickTime for Windows on the Apple Uninstall QuickTime (link is external)