Horizon Hobby reports the following,

"We have seen several e-mails from Chinese vendors offering the  Spektrum AR6100 and AR6100E at very low prices. These receivers are not  original Spektrum receivers, but are counterfeit copies, not  manufactured by Spektrum, and they do not use our specified components.
Consumers are cautioned to make sure they are purchasing original  Spektrum receivers in original packaging. Counterfeiters have the  ability to make very visually similar copies, so unfortunately there is  no way to easily distinguish between originals and copies. The best  thing that consumers can do is to make sure they are purchasing their  products from established  hobby and model shops (http://www.horizonhobby.com/StoreLocator) who buy directly from Horizon Hobby or from  one of our international  distributors (http://www.horizonhobby.com/StoreLocator/Default.aspx?Tab=Int).
In addition, some websites are now offering receivers that claim  compatibility with Spektrum or DSM2 technology. Horizon Hobby and our  Spektrum team have not certified or authorized any other company’s claim  of compatibility.
Horizon Hobby disclaims any and all liability for any damages or  claims arising from the use of any counterfeit Spektrum receiver or any  non-Spektrum or JR receiver claiming DSM2 compatibility. The consumer  assumes all liability for using such products.
Horizon’s is always striving to ensure your enjoyment in the hobby by  developing and producing products to a tight standard of quality and  performance. Don’t put your enjoyment at risk by utilizing imitation or  untested generic components that could jeopardize the safety of your  flying experience." Horizon Hobby

*Horizon Hobby* (http://www.horizonhobby.com/)