Need a trustworthy Youtube to iMovie converter

OK, so I've concluded I just need to convert Youtube videos to iMovie. There's several websites saying how to do this and to download free software.

However, I hate just downloading software from the first website I see. None of the sites I've seen have I recognized as a credible, virus-free site. However, that doesn't mean much. Anyone have a recommendation for me? Good website and/or software?

Thanks!