Instagram, the popular photo-sharing app, is having the best week of its short existence. In the wake of announcing Facebook will acquire the app in a billion-dollar deal, Instagram's new Android app surged to 5 million downloads little more than 5 days.

Prior to the Facebook purchase, Instagram was rumored to be raising a massive wad of cash in a second round of funding. Rumors about the latest round indicated that the company had closed $50 million second round, leaving the company at a $500 million valuation. That number was quickly doubled when Facebook bought the company for about $1 billion in cash and stock.

I'm excited to share the news that we've agreed to acquire Instagram and that their talented team will be joining Facebook, said co-founder of Facebook, Mark Zuckerberg in a written statement. For years, we've focused on building the best experience for sharing photos with your friends and family. Now, we'll be able to work even more closely with the Instagram team to also offer the best experiences for sharing beautiful mobile photos with people based on your interests.

The founders of Instagram were similarly excited to share the news: When Mike and I started Instagram nearly two years ago, we set out to change and improve the way the world communicates and shares, said CEO of Instagram, Kevin Systrom. We've had an amazing time watching Instagram grow into a vibrant community of people from all around the globe. Today, we couldn't be happier to announce that Instagram has agreed to be acquired by Facebook.

In the days preceding the Instagram-Facebook deal, Instagram for Android had proven it was already a runaway success, racking up more than 1 million downloads in less than 24-hours. Systrom told the New York Times that the company was signing up more than 2,000 people a minute. That number apparently jumped even higher around the time of the Facebook purchase.

While some storied Instagram users have chosen to revolt against the photo-sharing app, Instagram appears to have opened itself to two very important user bases: The first is the number of Android users -- more than 300 million -- which have already boosted Instagram's user base significantly, hitting a mark it took the company nearly six months to hit on Apple's iOS. The second is the user base of Facebook, which was last cited at 845 million. Although it's highly unlikely that Facebook will require its users to download or use Instagram, the backing of the world's largest social network surely won't hurt the photo-sharing app. With Facebook rumored to be aiming for a $100 billion valuation following its IPO, Instagram has just been solidified its future and sale.