Credit reference and analytics company Experian, of Costa Mesa, Calif., has acquired internet marketing intelligence firm Hitwise, of New York, for about $240 million in cash.

Hitwise collects information about traffic to Web sites, getting it directly from internet service providers, and has done a good job marketing the information (they’re constantly sending us comparisons between Web 2.0 companies, for example, to help VentureBeat with reporting). It says it covers the surfing patterns of about 25 million people in the US, UK, Australia and the Asia Pacific.

Data has become more important, as advertisers and others seek more information about which sites they want to support and which ones have influence.

Hitwise reportedly raised less than $20 million since its founding in 1998. Insight Venture Partners was an investor, and told Dow Jones it owned about one-quarter of Hitwise, suggesting this was a great return. Sydney-based venture capital firm Allen & Buckeridge invested in a seed round.

Google is one of more than a thousand customers of the company.

More here from Tim O’Reilly about this, who talks about the significance of data.