• by Mark Walsh  @markfwal, January 17, 2013

Pushing back against reports of a steep drop in its user base, Instagram on Thursday said it now has 90 million monthly active users and is seeing growth rather than decline.

Reporting monthly usage for the first time,  the company told AllThingsD that total is up 10% in January from December.

The disclosure is the latest twist in a metrics squabble that kicked off when the New York Post reported last month that Instagram had lost a quarter of its active daily users following its Terms of Service debacle. That prompted a blogosphere backlash, pointing out the Post story relied on App Data figures which only track Instagram activity tied to users’ Facebook accounts.

Instagram also attacked the report’s accuracy, insisting it continued to see strong and steady growth in both registered and active users. Instagram parent Facebook subsequently pulled public access to the data used in the Post story. The update on monthly users Instagram issued today isn’t likely to end the contretemps, however.

For one thing, it didn’t provide any new data on daily active users, which was the crux of the initial metrics dispute. Why not? There’s also other third-party sources to turn to for a read on Instagram’s audience. comScore, for instance, has begun providing combined traffic data across the desktop, mobile Web and apps. Its January data isn’t available yet, but it’s another way to gauge whether Instagram's usage is growing, contracting or simply flat.