Uninstall Quicktime if you're using Windows, now
Security experts say that anyone using Apple's QuickTime on Windows needs to stop that, right away. It is reported that the software is vulnerable to two critical security flaws, and those vulnerabilities aren't going to be fixed, ever.
So, to avoid the threat of hacks and other grisly business, get it off your computer as soon as you can.
This comes from Trend Micro, who said that Apple has ‘deprecated’ (so, stopped developing and doing updates for) the Windows version of the software. If you're using QuickTime for Mac's OS X, you're fine and don't need to do anything.
For those of you who know about these things, the QuickTime flaws are both ‘heap corruption remote code execution’ vulnerabilities. Basically, these can be exploited by hackers who can do nasty things to your device with malicious code or whatever.
There's no known attacks like this, but there is potential for it. Chances are, you have barely used QuickTime too, so it isn't worth taking the risk. You could use VLC instead, for example, which is hugely popular.
Go to your 'Add or Remove Programs' menu on your computer, and proceed with the uninstall from there.