If you are running QuickTime for Windows on your personal computer, you should uninstall it as soon as possible.
The two vulnerabilities were disclosed publicly on Thursday without a patch because the Windows version of QuickTime is deprecated, i.e. it will no longer receive security updates.
An alert issued by the US Homeland Security's Computer Emergency Readiness Team (CERT) agrees that the threat is serious:
https://www.grahamcluley.com/2016/04/quicktime-windows/