Tumblr's ban on adult content went into effect Monday, and it didn't take long for users to bare their naked thoughts on the move.

The blogging platform announced the change Dec. 3 in a post titled "A better, more positive Tumblr." On Monday, a new post apologized for what the site admitted has "not been an easy transition." Flagged content will be hidden, not deleted, the site reported.

"Written content such as erotica, nudity related to political or newsworthy speech, and nudity found in art, specifically sculptures and illustrations, is also stuff that can be freely posted on Tumblr," the post says. "Although, photorealistic imagery or photography – images, videos, or GIFs -- with real humans that include exposed genitals or female-presenting (yeah, we know you hate this term) nipples or depict sex acts is not allowed per our guidelines."

Breastfeeding and nudity in art are still OK to post.

Users quickly found flaws in Tumblr's implementation of the ban. Some found tricks to get around the flagging process, others saw legitimate content hidden.

Asked for comment, Tumblr referred CNET back to the Dec. 3 and Dec. 17 posts, as well as the site's posted updates to its community guidelines.

this just in: porn bots on tumblr are evading being flagged/taken down by just straight up tagging their sexy posts as 'SFW' and it works

like, this is some Looney Tunes shit 2018 pic.twitter.com/JdnP8aoMcL — Girls and Gay (@InsomniaArrest) December 11, 2018

Images Tumblr users said were incorrectly hidden include:

Photos of cats, birds and rocks:

Pictures of my cat and photos of birds and rocks got flagged but i still had to block four porn bots yesterday #TumblrIsDeadParty #Tumblr — European Gay Disaster Girl (@kissesgrell) December 17, 2018

A pixelated Pokemon:

I'm doing #TumblrLogOff because their idiotic algorithm thought a text post with a single pixelated pokemon was NSFW. Thanks @tumblr, your already nigh-unusable site just got worse! — Duke (@laangdons) December 17, 2018

Mister Rogers and a mailman (was it Mr. "Speedy Delivery" McFeely?):

YOU FLAGGED A PICTURE OF MISTER ROGERS AND A MAILMAN!

That is all.

#TumblrProtest — Kaylee Fuhr (@KayleeFuhr) December 17, 2018

A photo of a pool:

hey @tumblr maybe you might want to listen to the people using your site, and actually ban literal nazis and pedophiles instead of "female-presenting nipples" and content you've deemed "nsfw" (how the fuck is my aesthetic picture of a pool nsfw?) #tumblrprotest #tumblrpurge — december chrimms time babeys :) (@AgentAngelace) December 17, 2018

A sleepy penguin:

Anyways tumblr is dead to me because they flagged these set of pictures pic.twitter.com/eqjED9mVTH — 🌙 litchi 🌙 (@suicunepng) December 16, 2018

A man's chest, but not when next to an owl:

So here's something. Users are testing the limits of Tumblr's new algorithm that flags adult content (aka "censorbot"). This one found that a man's chest was flagged, but a man's chest next a 50% scale owl went unnoticed.



Things seem to be going greathttps://t.co/FU1MudA0K9 pic.twitter.com/Tmm0JyPWJC — Chappell Ellison ٩( ᐛ )و✎ (@ChappellTracker) December 7, 2018

An ancient Egyptian tomb:

#Tumblr just flagged as "adult" this post I published relative to the recent archaeological discovery in Egypt … pic.twitter.com/nqARBqEcMf — bittenapple (@bittenapple) December 16, 2018

This cosplay tutorial:

My most popular #cosplay tutorial was flagged on Tumblr as inappropriate... What are they smoking over there? pic.twitter.com/OpgWOTQRoN — Quinn-tessential (@HorrorShadows) December 17, 2018

The items on this list, which includes "a puppy" and "leather boots":

Things that were flagged on @tumblr:

-Smoke art

-BNHA fanart

-A field of flowers

-woman in cosplay

-leather boots

-men kissing

-A puppy

-Fat sphinx cat

Things that weren't flagged:

-75% of the nsfw content on my side blog

-Bots

-Literal NAZIS

FIX YOUR SHIT TUMBLR.#TumblrLogOff — Snow F. (@SnowySpaceship) December 17, 2018

And even Tumblr's own post announcing the ban:

#tumblrpurge remember when THEIR OWN POST ANNOUNCING THE BAN WAS FLAGGED

Yeah

The only people arguing that #tumblr staff know what theyre doing is the staff themselves #tumblrban #tumblrpurge #tumblrboycott pic.twitter.com/o8sAlcIP2r — Team True Alpha ⭕️ (@VOlDlAS) December 17, 2018

The term "female-presenting nipples," mentioned in the Tumblr post about images that aren't allowed, came in for special ridicule from users, especially for the way the site acknowledged the term was problematic.

tumblr users: "hey guys, if you could do something about the pedophiles, porn bots, and white supremacists, that would be great."

tumblr staff: "ban the female nipple but let the nazis stay. got it. 👌"

users: "no, that's not what–"

staff: "w e g o t i t 👌👌👌"#TumblrLogOff — beam me up, guy (@cali4niaenglsh) December 17, 2018

not the best look for tumblr to try cutesily distancing itself from "female-presenting nipples" while actually doubling down on it pic.twitter.com/nCQnHLLUgC — Rave Sashayed (@_sashayed) December 17, 2018

the problem isn't that We Hate That Term;), although it's stupid and we do, it's that the whole idea that the female body is inherently sexual is Fucked Up And Bad, yall — Rave Sashayed (@_sashayed) December 17, 2018

maybe the real female-presenting nipples were the friends we met along the way pic.twitter.com/UdyMRZoCzV — Animated Text (@animatedtext) December 10, 2018

Today, we mourn the loss of female presenting nipples, but celebrate their legacy.. #tumblr — 🧛🏻‍♀️Nicole Maines🧛🏻‍♀️ (@NicoleAMaines) December 17, 2018

Prudishness aside, can we address the hyphen? It implies the nipples are presenting the females. — Sad Lieutenant (@unocajone) December 17, 2018

Hashtags including #TumblrLogOff, #TumblrPurge, #TumblrIsDeadParty and #TumblrProtest objected to the way the changes were being implemented, and some urged users to stay off the site for 24 hours in protest.

#tumblrprotest if you are boycotting tomorrow make sure to pass the plan around pic.twitter.com/4pXpsp23RK — Angharad Griffiths (@Angiepose) December 16, 2018

I’m officially off #Tumblr for the next 24hrs in protest of their new policy changes that do nothing to stop porn bots & child predators but do harm artists, gamers, social justice blogs, body positivy blogs & many others #TumblrLogOff — LevelUpLynn 🦄 (@LevelUpLynn) December 17, 2018

Signed out of @Tumblr for 24 hours. If they're going to crash and sink their own ship, might as well make it go ALL THE WAY DOWN. #TumblrIsDeadParty — Merry Impmas (@ImperfectXIII) December 17, 2018

In a fairly meta move, some people posted their Tumblr issues on Tumblr itself.

Although the ban may have been well-intentioned, many users clearly disagreed with how it was implemented.

#tumblr #tumblrisdeadparty



"We did it! We fixed our site by deleting all the porn!" pic.twitter.com/fu8fmkZ3eV — Takashi Shirogane (@Starry_Paladin) December 3, 2018

First published Dec. 17, 11:18 a.m. PT.

Update, Dec. 17 at 11:57 a.m. PT: Adds response from Tumblr.

Update, Dec, 17 at 12:17 p.m. PT: Adds Tumblr user posts relating to ban.