The risk of this is minimal, since most odesk workers just want to make money by doing work and have no interest in stealing your business model.
I would advise not just posting a job to odesk out in the open as you will get loads of unqualified workers begging to do work for you. Instead, create a job and then browse the profiles of people with experience (unless you want to spend weeks training someone).
It pays to get someone experienced even if they cost more, it will save you money in the long run!
The best thing to do if you are worried about account stealing etc. is to have different people doing different things, which spreads the risk. Also look for good feedback.
This is just from my experience of using odesk, I don't use odesk any more i tend to use another provider which seems to be just good enough for my needs (pm me if you want the name of them)