Twitter is accusing Microsoft of using the social media company's data in ways that were unauthorized and never disclosed. However, for one of the Microsoft services using Twitter data, "account information outright states that it intends to allow its customers to 'go around throttling limits,'" Spiro wrote. A Microsoft spokesperson acknowledged receipt of the letter and told CNBC the company will review it and "respond appropriately." "Today we heard from a law firm representing Twitter with some questions about our previous use of the free Twitter API," the spokesperson said in an email. Read the full letter from Twitter to Microsoft, here.

---