They are considered to be and listed as an "Alternative Metal" and/or "Nu-Metal" band!
True... the genre "Hard Rock" is mentioned in the Wiki article, but that's where it ends... In my (humble) opinion, "Hard Rock" is like it's described best in the Wiki article about it :
"Hard rock maintained a bluesy rock and roll identity, including some swing in the back beat and riffs that tended to outline chord progressions in their hooks"
Whereas "Alternative Metal" and/or "Nu-Metal" are best described as :
"A sub-genre of Heavy Metal, with more volume and distortion used combined with aggressive riffs with pop structures and a drawing influence from a variety of genres within and outside of heavy metal"
Basically saying... There's the genre of "Hard Rock" and the genre of an even harder "Nu-Metal"!
I'm with Nicho on this one. Disturbed can be considered hard rock. As a matter of fact, in my opinion Disturbed is more hard rock than metal. Of their albums: Indestructible is straight-up Hard Rock. Believe is mainly hard rock. Ten Thousand Fists is also pretty much hard rock. The Sickness is mostly nu-metal. Asylum is alternative metal.
3 out of their 5 albums are mainly hard rock, that makes them a hard rock band.
Finally, let me quote wikipedia: When asked about die-hard heavy metal fans not finding Disturbed heavy enough, Draiman at one time stated: "We probably have too much melody going on or we're not quite as turbulent or caustic. While I really love that type of music, it's not what we try to do. If we have to place things in context, we're more hard rock than heavy metal these days."
Anyways, Disturbed is not really one of the bands that fit nicely into one category. They are a bit of everything.
So they are a strayed dog on out the streets of the harsh music world so to speak? They won't fit in with any family of music genre, but do go on and continue making their own style of music! Fair enough! I stand corrected then... =)