I wouldn't say Disturbed stole it. Every band in one way, shape or form is influenced by another. You look at bands like Metallica and Megadeth who are both heavily influenced by Black Sabbath and then when you move to present day bands like Trivium and Avenged Sevenfold are heavily influenced by Megadeth and Metallica. Many people complain about bands using material from other bands before them but it won't stop anytime soon nor should it, you need to stay true to your influences that brought you to the dance so to speak, that's why there can be alot of references from the sickness to early work done by Korn, possibly one of Disturbed's biggest influences to date. So in the end people will tell you that it's stolen but you can't copyright a riff, end of story.