Jack Dorsey and Christopher "Biz" Stone are deemed inventors by the USPTO, who were granted patents to the way their creation, Twitter works: a messaging system where people follow each other, and make messages not directed to any unique recipient, but their followers. Patent # 8401009 details what Twitter just scored.
What does this mean for the various Twitter knock-offs? Around this time last year, Twitter announced its Innovators Patent Agreement, which promises its employees to use its patents only defensively. Major social network competitors like Facebook and Google+ will now have to comb through their services to check if they've made the blue bird angry.