I asked the same question yesterday and it seems that FB acquired Onavo. They joined this data with the rest of their user data, and then used it to make anti-competitive decisions.

It'd be like if Apple bought Appannie, matched the behavior with their existing customer database, and then used the data to delist Spotify from their app store because it competes with iTunes.

That’s messed up sure, and I am not a lawyer, but I don’t think how they got the information to act in an anticompetitive way is relevant, in the US at least (as long as it was legal, which buying up smaller companies is). Am I missing something? Is it fraud because they continued to market the vpn service as being private while they used it to collect market research data for facebook?

I think that maybe it's because Onavo acquired the information with a specific agreement with it's users, which didn't cover the way Facebook used it after FB acquired the agency, but then again, I'm not sure.

SOP for these situations is to license the data from the agency, so you can say that you're using third-party data which is also available to your competition. Level playing field and all that. Acquiring the entire company is a risk because it closes it off to competition and isn't necessary to just use the data.