It represents the company's biggest move yet to become a major player in online advertising.
The agreement gives CBS one of the most heavily trafficked collections of web properties.
They include News.com, ZDNet, Game Spot, the music destination site mp3.com and a series of entertainment and information venues.
CBS said it would combine these with its existing internet properties, making it one of the top US web companies, with 54 million monthly users.
CNET was one of the largest remaining independent content properties, with a reported revenue of $405 million last year.