Trend Micro have identified 2 security flaws in the latest version of QuickTime for Windows. Both of these flaws that have been identified allow for remote code execution, which means that whoever takes advantage of this flaw can run anything that they want on your computer. (see Trend Micro's Blog)
Since Apple has stopped providing updates to QuickTime for Windows, these flaws will never be fixed nor any further flaws that are identified.
The US Government and multiple industry experts are advising that the program be uninstalled IMMEDIATELY to secure your computer.
You can find instructions for removing QuickTime on Apple's web site - https://support.apple.com/en-au/HT205771
While Apple are still supporting QuickTime for MAC OS, they have stopped developing the product for Windows.
The downside of Apple dropping support for QuickTime is that there are a number of other packages that require QuickTime to run.
In the past QuickTime was needed to play back videos in iTunes, but iTunes no longer requires QuickTime for video playback. To playback QuickTime movies, there are alternatives like VLC Media Player