Tumblr's sudden disappearance from the iOS App Store on Friday — still unresolved — was because material slipped through the blogging network's child pornography filters, according to the company.

"Every image uploaded to Tumblr is scanned against an industry database of known child sexual abuse material, and images that are detected never reach the platform," it said in a support update. "A routine audit discovered content on our platform that had not yet been included in the industry database. We immediately removed this content."

Work continues on returning Tumblr to the App Store, the company said, without saying what changes are being made or an expected timeframe. For reasons unknown the app remains available on Google Play for Android devices.

Apple has adopted a zero-tolerance policy, choosing to pull any app with accessible child pornography even when it may be hard to find and developers are continuously trying to root it out. Another example is in February, when the popular messaging app Telegram was pulled. Apple worked with Telegram to get the illegal content taken down, ban the offending users, and institute controls.