Twitter is acquiring a small password security startup called Mitro for its New York office. Mitro built a way that multiple people can share or control passwords to a single account.

The most obvious use case would have been in the enterprise where team members need to share a single password for an account. Twitter isn’t keeping the product and we hear that the team will likely be working on geo-location products.

However, unlike in previous acquisitions, Twitter is allowing the product to live on. Mitro is becoming an open source project and the startup is working with the Electronic Frontier Foundation to vet the code and guide Mitro toward being a self-sustaining, nonprofit, community-run service. For now, it will stay available until at least the end of the year. The company has released all of Mitro’s server and client code under the GPL license on GitHub.

This is different from an earlier Twitter acquisition. When the company acquired Posterous, it shut down the product, so co-founder and now current Y Combinator partner Garry Tan built an equivalent called Posthaven so that Posterous users could have an alternative when the product died. It seems that acquirers doing talent hires are starting to offer founders more flexibility in sustaining their work independently if the products are not of strategic value.

Mitro was backed by $1.2 million in seed funding from Google Ventures and Matrix Partners.