Facebook is tightening its rules around the use of raw, device-level data used for measuring ad campaigns that Facebook shares with an elite group of advertising technology partners. The company recently tweaked the terms of service that apply to its “advanced mobile measurement partner” program, which advertisers tap into to track the performance of their ads on Facebook. Those mobile measurement partners (MMPs) were, until now, free to share the raw data they accessed from Facebook with advertisers. These metrics drilled down to the individual device level, which advertisers could then reportedly connect to any device IDs they might already have on tap. Facebook reportedly began notifying affected partners on February 5 and all advertising partners must agree to the updated terms of the program before April 22.