I don't know. But I do know that the way to prevent that is to handcuff all the developers with crushing process heaviness. Then they won't introduce anything malicious, because they won't introduce anything at all.
“The Cupertino, California-based company said in a lengthy memo posted to its internal blog that it "caught 29 leakers," last year and noted that 12 of those were arrested. "These people not only lose their jobs, they can face extreme difficulty finding employment elsewhere," Apple added.”
https://www.bloomberg.com/amp/news/articles/2018-04-13/apple...
Bloomberg.