Possible GPL violation by humax-digital product: "i cord HD"

[web2001 at worldonline.de]

Hi,

Humax Digital (http://www.humax-digital.de) is a german vendor of 
digital set-top-boxes (also known as receivers).
One of the newer models by humax-digital (the "icord hd") uses Linux as 
the operating system.
The Box is on the market since 12/2007 and the source code has not been 
released yet.
The support of the company says that the decison about the release of 
the source code has not been made yet.
But I think they must release the source code or isn't linux under the GPL?

Best Regards

C.Schmitt