The company said that the patent on its zCast technology brings its total number of patents to about 50.
But one analyst says it's likely that many of those patents are no longer valuable.
"I think the fact that (NetZero has) gotten a patent is a good thing," said Gartner analyst Lydia Leong. But "I wouldn't necessarily say it's an advantage over anybody, particularly since most of the competitors are going out of business."
NetZero chief executive Mark Goldston said the patent will have a positive affect on the company.
"This will put NetZero...in a very long tradition as (tending) the business model that we pioneered," Goldston said.
Free ISPs recently have faced numerous hurdles, such high costs for acquiring subscribers, massive turnover, and ongoing questions about consumer tolerance for advertising, which typically pays the bills on such services.
NetZero's announcement comes as a string of rivals are closing their doors.
Kmart's BlueLight.com said Monday that it is acquiring the Internet service assets of free ISP Spinway.com. CMGI said it would close its majority-owned free ISP 1stUp.com, a move that has forced CMGI-owned AltaVista to shutter its own branded free ISP.
In July, Juno Online Services purchased pieces of failed rivals Freewwweb and WorldSpy.
NetZero has made a similar move, signing a subscriber referral agreement with free access provider iFreedom.com.