From the San Francisco Chronicle:

The widespread Internet posting of a letter by a retired Purdue University researcher who says he has linked genetically modified corn and soybeans to crop diseases and abortions and infertility in livestock has raised concern among scientists that the public will believe his unsupported claim is true.

The letter to Agriculture Secretary Tom Vilsack has been posted on dozens of websites ranging from the Huffington Post to obscure gardening and food blogs, generating discussion on message boards about the controversial topic of genetically modified crops and their potential effect on animals and humans.

But other scientists say they have no way to verify professor emeritus Don Huber's claims because he won't provide evidence to back them up.
Huber, 76, wrote the letter to Vilsack in January, warning of a new organism he claims has been found in corn and soybeans modified to resist the weed killer Roundup. Huber wrote that the organism could lead to a "general collapse of our critical agriculture infrastructure" and further approval of Roundup Ready crops "could be a calamity."

For more, see: Scientists question claims in biotech letter