Recap: There are several reasons why a website might suddenly see a drastic decrease in traffic, one of which is the removal of all the porn. That's what happened to microblogging site Tumblr, whose ban on adult content in December saw its viewer figures plummet.

According to web analytics firm SimilarWeb, via The Next Web, Tumblr had 521 million page views in December. Thirty days later, that figure was down to 437 million---a near 100 million drop that represented a 17 percent decline in viewers.

Tumblr's decision to remove virtually all adult material from the site--- educational, newsworthy, or political nudity are still "fine"---was a reaction, or some would say overreaction, to the app disappearing from the App Store after the discovery of child pornography on the platform.

In November last year, there was confusion over why Tumblr had vanished from Apple's store. A spokesperson for the site later explained that it kept child pornography off the service by scanning every image "against an industry database of child sexual abuse material." A routine audit discovered content that had not yet been added to this database, allowing it to pass through Tumblr's image filter.

Tumblr removed the offensive content, but the service went one step further and announced it would ban all adult material. Two weeks later, it was restored to the App Store.

Before the ban, users were warned before accessing adult-only blogs that contained sensitive material.

A petition was started to make Tumblr reverse its decision. So far, it has received over 602,000 signatures toward the 1 million target. "Let people post porn, it's 90 per cent of the reason anybody is on the site in the first place," it states. Whether the campaign and lost users prompt a rethink on Tumblr's part remains to be seen.

Update: Responding to the report, a Tumblr spokesperson said: "We made a strategic decision for the business that better positions it for long-term growth among more types of users. This was the right decision."