I suspect you will find both .qt & .mov files are spam. Most often porn spam. Personally I added both .mov & .qt to the Keyword filter list in LW's preferences.

However to answer your question, if VLC cannot play those files then they are just bad files. I started to answer this question but was called away for an hour. No need for me to post the link again lol. ukbobboy01 gave a great answer!

I would also highly recommend this http://perian.org/ for quicktime. It adds a lot of support for QT Player such as DivX, 3ivx, Flash, AVI, MKV, Windows Media Audio v1 & v2, DTS, AAC, AC3 Audio, subtitles, etc.

VLC is also a very good to check the validity of audio files with. So if a song won't play with iTunes then try it with VLC. If VLC cannot open it then it's a dud file.

One thing VLC does which protects you, is some video files are laced with http weblinks that take you to some dangerous website. VLC will not open those links, whereas QT Player will attempt to!

On my mac, I have some kinds of files I set to open with VLC by default, some with QT. I manually change them for specific files sometimes.