The New York Times Co. ( NYT) said Thursday that it was buying the About.com Web site from Primedia ( PRM) for $410 million in cash.

The Times said the deal would help the company increase its reach among online users and help diversify its online advertising base.

The deal is the latest example of major media companies buying up Internet properties to increase their exposure to the fast-growing online advertising business. Recently, Washington Post Co. ( WPO) bought the online magazine Slate from Microsoft ( MSFT). Earlier this year, Dow Jones ( DJ) completed its acquisition of financial news publisher MarketWatch.

Primedia, which purchased About.com in 2001 for about $430 million in stock, had been shopping the online operation around for bids, it was reported earlier this month .

Citing statistics from Nielsen//NetRatings, the Times said that About.com, which reaches 22 million monthly users, will combine with the Times' current base of 13 million users to form the 12th-largest company on the Internet.

Separately, the Times said it was promoting longtime digital media executive Martin Nisenholtz to the post of senior vice president of digital operations.

Primedia's shares jumped 35 cents after hours to $4.40. Times shares ended regular trading at $38.25, down 46 cents.