Facebook has landed another promising startup, sealing a $16 billion deal with WhatsApp.

Mark Zuckerberg and company have agreed to purchase the messaging service for $16 billion in cash and stock, making the transaction the largest-ever in startup history, The Wall Street Journal reported.

WhatsApp is essentially a free text messaging service and has seen its users more than double in the past nine months to 450 million, a number substantially higher than Twitter's 240 million active accounts.

Founded in 2009, the company has 55 employees with only 32 engineers and no marketing or public relations staff. WhatsApp has had something of a meteoric rise, garnering its 450 million users faster than any other company in history, WSJ reported.

The app, which is used to send around 50 billion messages daily, allows users to message text, pictures and video to any other users.

While WhatsApp is definitely popular, what's less clear is how the service will make money for Facebook. The messaging app doesn't have ads and only charges 99 cents annually to users after their first year.

A refreshing aspect to the company, which was founded by Ukrainian Jan Koum and American Brian Acton, is its vigilance for user privacy. Messages are deleted from the company's servers after they're delivered, giving WhatsApp little to offer to government agencies or anyone else who wants to track users.

Based in Mountain View, Calif., WhatsApp was reportedly wooed by Google several years ago, and the two companies recently talked again about a possible deal. A Google spokesman declined to comment to WSJ.

Facebook's deal with WhatsApp dwarfs its 2012 purchase of Instagram for $1 billion. The social network also reportedly tried to purchase Snapchat last year for $3 billion but was turned down.

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