The WhatsApp founders were the big winners in their recent Facebook acquisition, cashing-in on nearly $9 billion worth of Facebook stock. Regulatory filings released on Wednesday show that Jan Koum and Brian Acton hit the jackpot receiving a combined 116 million Facebook shares. The founders sold their mobile messaging service to the social networking giant last month and are now reaping the rewards. Koum, a Ukrainian immigrant who was once living on welfare, is now the fourth largest Facebook stockholder, with a fortune worth around $5.8 billion. Acton, a former engineer at Yahoo owns shares reportedly worth a further $3 billion. Around 45 other WhatsApp employees also received Facebook stock.