Financial firms are technology organisations, and all such organisations need to worry about Intellectual Property Risk. IP Leakage can happen anywhere.
Arguably, risks are greater in finance because of the penalties that regulators may apply.
Historically, use of social media / sharing sites has been prohibited by many firms to mitigate data leakage.
But you have to balance the data leakage risk against the benefits (outlined above). Therefore: can employees use a site like GitHub (where uploading data is commonplace) but have controls in place to mitigate the data-leakage aspect?
Tools such as GitProxy, personal machines, ephemeral desktops etc. help to mitigate this.
Training of open source developers within the organisation is an important step. Do developers understand the rules? Can you be explicit about what is and isn't included in a commit? For example: non-code contributions such as test data might be outside the policy. It's easier to have a blanket policy that this isn't allowed. Test data needs to be generated by the tests as they run instead.
A governance process needs to be in place for supervising contributions and observing what leaves the organisation.
Tools like GitHub Enterprise also aim to help with Data Leakage Prevention.
Evidence may need to be provided that data hasn't been leaked (according to regulations).