I got an offer from the WorldQuant's Moscow branch some months ago, and everything was good until I decided to accept it. I was unable to sign the papers right away because I needed to know the exact day of my graduation from my university. So we agreed (via email and orally) to wait until my exact starting date is known.
When the time came I contacted WorldQuant's HR in order to actually sign the contract, and was told that my job offer was cancelled. Since they didn't support their decision by any arguments (e.g. my violation of preliminary agreements, the company policy, laws, e.t.c.) the refusal is just their caprice.
So guys, be aware that this company can give you a job offer and then cancel it without any reason.