Instagram has 100 million users

"Now, nearly two and a half years later, over 100 million people use Instagram every month. It’s easy to see this as an accomplishment for a company, but I think the truth is that it’s an accomplishment for our community. Now, more than ever, people are capturing the world in real-time using Instagram—sharing images from the farthest corners of the globe. What we see as a result is a world more connected and understood through photographs."
Source:  Instagram blog, 26th February 2013
Note - this is where it gets complicated:
In Sept 2012 Mark Zuckerberg announced 100m users, and The Next Web did this handy table of its growth since launch.
However, those were only the number of registered users - and many people download apps and don't use them regularly.
The nearest comparable figure is this statement from Instagram that they had 90m monthly users from early February 2013 - so they've gained 10m in a month.  So much for privacy concerns!