Ning, the white-label social networking service, founded by Netscape founder Marc Andreessen, has raised a huge $44 million third round, among the biggest social networking raises thus far. The news was confirmed by Marc on his blog here. The round was led by the hedge fund Legg Mason with a number of other investors participating, including Marc himself.

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The round was orchestrated by Allen & Co, whose big and private conference is happening in Sun Valley, Idaho this week. That explains why Marc is attending the conference.

Ning was founded by Marc and CEO Gina Bianchini about two years ago, and has received two small rounds from “Marc and his friends”. The company had languished after its first release last year, but an update of its platform in February this year seems to have moved the needle, the company says. The new money will be used in “scaling our operations to accommodate our traffic and growth; in our product design and development efforts; and in our platform evangelism and support programs.” Whatever said and done, that amount is crazy money…and the pre-money valuation of about $170 million or so being bandied around is about right, our sources tell us.