On April 14, 2016, the US Department of Homeland Security issued an alert for anyone running Apple's QuickTime software on Windows systems to uninstall the program immediately.
Security vulnerabilities continue to surface in the QuickTime program, including two critical ones recently announced that could allow criminals to hack into systems with QuickTime installed if the subject system users either run malware or visit a malicious webpage, which a criminal can induce via phishing. Without ongoing security patches being issued by Apple, QuickTime software poses a serious danger to anyone running the program.
QuickTime for Windows is still available for download, and will still work as it did before, but it creates potentially serious vulnerabilities and should not be used - certainly not on computers connected to the Internet. The Department of Homeland Security alert was pretty blunt about how to protect oneself: "The only mitigation available is to uninstall QuickTime for Windows."
QuickTime can easily be removed from the system by following the standard Windows software removal process which should be done as soon as possible, especially if the system if connected to the Internet. If you are not sure if you have QuickTime installed just follow the standard removal instructions and look for QuickTime in the list of installed applications.