I've built several successful MVP's with contractor labor and I've worked at an agency where we built prototypes for entrepreneurs and companies. My experience is that working with any form of agency is not advisable for an MVP, but not because of security concerns (as others have already addressed).

An MVP will inevitably require multiple iterations to achieve product/market fit or provide you enough data to run a different experiment.

I built the site http://www.tellyourbossanything.com for less than $5,000 in contractor expenses and was lucky to get a ton of high quality press the first few days of launch that brought a few thousand users to us in the first week.

From there, we invested more money to iterate and build. No agency would have been able to iterate fast enough or efficiently enough post MVP.

I would advise that you look for a contract designer and a contract engineer (or two) to work with you. If you're unsure of whether you're qualified to manage these resources or where to look, happy to do a call with you!