The Huffington post claims Chertoff's company was doing undisclosed public PR for Rapiscan's equipment in The Washington Post, etc. misrepresenting the capabilities of their equipment, which the WP partially confirmed: http://www.washingtonpost.com/wp-dyn/content/article/2009/12...
Rapiscan denies that they hired him to as a government lobbyist, so they're very specifically denying something other than what they're being accused of.
Rapiscan (the scanner subsidiary of OSI) rebutted the claims: http://www.rapiscansystems.com/en/the-checkpoint/article/the...