The dial-up dinosaur United Online Inc. is spinning off its revenue generating media Web sites into a separate public company.

Classmates Media Corp., a wholly-owned subsidiary of Woodland Hills-based United Online, filed for an initial public offering last week. The company mainly runs social networking site Classmates.com and MyPoints.com, a loyalty marketing service provider.

Classmates Media is hoping to raise $125 million in the offering and plans to trade on Nasdaq. Goldman Sachs & Co., Deutsch Bank Securities and JPMorgan are underwriters for the offering.

The company did not disclose the percentage of shares United Online will own following the offering, but analyst Ali Mogharabi of B. Riley & Co. estimates the company will own about 80 percent of Classmates’ shares. This would translate to a valuation of more than $600 million.

“It’s a move to unlock the value of United Online’s content and media business. The value of the business has been hidden under the entire company,” Mogharabi said. “The perception is that United Online is just a dial-up access business. The growing media side of the business hasn’t been seen.”

Classmates Media reported in its SEC filings that revenues surged 64 percent in 2006 to $139 million. During the first quarter, sales jumped by 69 percent to $42.4 million.

United Online, which formed in 2001 with the merger of Juno and NetZero, is a $522 million operator of dial-up Internet service a technologically archaic but a profitable business.

It’s an industry that continues to lose ground to broadband and wireless offerings and to offset the declines, United Online bought Classmates.com in 2004 and MyPoints.com in 2006. Together, they generate about 40 percent of the parent company’s revenue.

United Online’s investors seemed pleased with the company’s move. Shares gained about 8 percent to $14.50 a share Tuesday then tapered off to about $13 on Wednesday and Thursday.