For anyone wondering, if you want to remove a file or secret you've already committed, you can use BFG Repo-Cleaner to go through your commit history and completely remove any trace of it. https://rtyley.github.io/bfg-repo-cleaner/
http://jordan-wright.com/blog/2014/12/30/why-deleting-sensit...
The top HN comment on the article details their experiences with getting hacked this way: