CoD+Skins=ban?!

[CWMV]

So Im reading and hearing conflicting things about this.
Ive seen more than a few very nice third party skins for CoD out there, many of them here, but Ive read too that using these skins will get your steam account locked? what the heck?
But I see two different types of skins out there too, some like IL2 seem to be little more than pictures in a certain format, while others seem to be in the form of a modpack. Is there a difference between these? Will one get you locked and not the other or is what Ive read and heard about this a bunch of nonsense?