Social media giant Facebook has announced that it has purchased popular mobile messaging company WhatsApp for a whopping 19 billion dollars. It is the largest acquisition by the Mark Zuckerberg-led firm so far that will give it a stronghold in the market for messaging. WhatsApp hasmore than 450 million monthly users. The whopping acquisition price includes 4 billion dollars in cash, about 12 billion dollars worth of Facebook shares and 3 billion dollars in restricted stock units to be granted to WhatsApp's founders and employees that will vest over four years following the closing of the deal. Under the agreement, WhatsApp co-founder and CEO Jan Koum will join Facebook Board of Directors. Facebook said the acquisition will not impact the WhatsApp's brand, which will be maintained and the company's headquarters will remain in California's Mountain View. WhatsApp's core messaging product and Facebook's existing messenger app will continue to operate as standalone applications.