Shadow banning (also called stealth banning, ghost banning or comment ghosting) is the act of blocking or partially blocking a user or their content from an online community such that it will not be readily apparent to the user that they have been banned.
By making a user's contributions invisible or less prominent to other members of the service, the hope may be that in the absence of reactions to their comments, the problematic or otherwise out-of-favour user will become bored or frustrated and leave the site.
In the mid-1980s, BBS forums including Citadel BBS software had a "twit bit" for problematic users. When enabled, the user would have limited access, and commonly still be able to read public discussions; however, any messages posted by that "twit" would be not shown to the other users.
Michael Pryor of Fog Creek Software described stealth banning for online forums in 2006, saying how such a system was in place in the project management system FogBugz, "to solve the problem of how do you get the person to go away and leave you alone". As well as preventing problem users from engaging in flame wars, the system also discouraged spammers, who if they returned to the site would be under the false impression that their spam was still in place. The Verge describes it as "one of the oldest moderation tricks in the book", noting that early versions of vBulletin had a global ignore list known as "Tachy goes to Coventry", as in the British expression "to send someone to Coventry", meaning to ignore them and pretend they don't exist.
Craigslist has also been known to "ghost" a user's individual ads, whereby the poster gets a confirmation email and may view the ad in their account, but the ad fails to show up in the appropriate category page.
Early on, Reddit implemented a similar feature, initially designed to address spam accounts, though it is also used for general users. In 2015, Reddit added an account suspension feature, though the site still makes extensive use of shadow banning.
In a study that looked at tweets from 2014 to early 2015, over a quarter million tweets were found during the one year period in Turkey to have been censored via shadow banning. Twitter was also found, in 2015, to shadowban tweets containing leaked documents in the US.
"Shadow banning" became popularized in 2018 as a conspiracy theory that Twitter had shadow-banned Republicans  In late July 2018, Vice News found that several supporters of the US Republican Party no longer appeared in the auto-populated drop-down search menu on Twitter, thus limiting their visibility when being searched for - allegedly due to the same algorithm that was being used to do the same to the accounts of prominent racists.  After that finding, some conservatives accused Twitter of enacting a shadowban on Republican accounts, which Twitter flatly denied. However, some accounts that were not overtly political or conservative apparently had the same algorithm applied to them.  In a blog post, Twitter said that the use of the phrase "shadow banning" was inaccurate, as the tweets were still visible by navigating to the home page of the relevant account. Later, Twitter restored the affected accounts.
- Thompson, Clive (29 March 2009). "Clive Thompson on the Taming of Comment Trolls". Wired magazine. Retrieved 6 July 2014.
- Robert Walsh (12 January 2006). Micro-ISV: From Vision to Reality. Apress. p. 183. ISBN 978-1-4302-0114-4.
So one of the things we did in FogBugz to solve the problem of how do you get the person to go away and leave you alone is, well, you take their post and make it invisible to everyone else, but they still see it. They won’t know they’ve been deleted. There’s no one fanning their flame. You can’t get into a flame war if no one responds to your criticism. So they get silenced and eventually just go away. We have several ways of telling if they come back, and it’s been proven to be extremely, extremely effective. Say a spammer posts to your board and then they come back to check if it’s still there, and they see it—to them it’s still there—but no one else sees it, so they’re not bothered by it.
- "Where Did the Concept of 'Shadow Banning' Come From?". Motherboard. 2018-07-31. Retrieved 2018-08-01.
- Atwood, Jeff. "Suspension, Ban or Hellban?". Coding Horror blog. Retrieved 17 December 2011.
- "Manual installation of Citadel using source code and the command line client - Citadel.org". www.citadel.org. Retrieved 10 March 2017.
- Bohn, Dieter (2017-02-16). "One of Twitter's new anti-abuse measures is the oldest trick in the forum moderation book". The Verge. Retrieved 2017-02-17.
- Leena Rao (May 18, 2013). "The Evolution of Hacker News". TechCrunch. Retrieved 10 August 2014.
- "Can the democratic power of a platform like Hacker News be applied to products?". Pando. 2013-12-04. Retrieved 2018-08-01.
- "How to Prevent Ghost Posting on Craigslist". Small Business - Chron.com.
- "One App, Two Systems: How WeChat uses one censorship policy in China and another internationally - The Citizen Lab". The Citizen Lab. 2016-11-30. Retrieved 2017-04-29.
- krispykrackers. "On shadowbans. • r/self". Reddit.
- Shu, Catherine. "Reddit Replaces Its Confusing Shadowban System With Account Suspensions". TechCrunch. Retrieved 16 September 2017.
- "China's We Chat "shadow-bans" messages with forbidden keywords, but only for China-based accounts". Boing Boing. Retrieved 2017-04-29.
- "One App, Two Systems: How WeChat uses one censorship policy in China and another internationally - The Citizen Lab". The Citizen Lab. 2016-11-30. Retrieved 2018-08-01.
- Tanash, Rima S.; Chen, Zhouhan; Thakur, Tanmay; Wallach, Dan S.; Subramanian, Devika (2015-01-01). "Known Unknowns: An Analysis of Twitter Censorship in Turkey". Proceedings of the 14th ACM Workshop on Privacy in the Electronic Society. WPES '15. New York, NY, USA: ACM: 11–20. doi:10.1145/2808138.2808147. ISBN 9781450338202.
- Ohlheiser, Abby; Ohlheiser, Abby (2015-10-30). "Tweets are disappearing on Twitter. Why?". The Washington Post. ISSN 0190-8286. Retrieved 2017-04-29.
- "Is Twitter Censoring a Blockbuster Report on US Drone Assassinations?". Motherboard. Retrieved 2017-07-26.
- Lorenz, Taylor (June 7, 2017). "Instagram's "shadowban," explained: How to tell if Instagram is secretly blacklisting your posts". Mic Network Inc. Retrieved 2017-11-04.
- Wong, Kristin. "How to See If Your Instagram Posts Have Been Shadowbanned". Lifehacker. Retrieved 2017-11-04.
- "Photographers Claim Instagram is 'Shadow Banning' Their Accounts". PetaPixel. 2017-03-28. Retrieved 2017-04-26.
- Romano, Aja (6 September 2018). "How hysteria over Twitter shadow-banning led to a bizarre congressional hearing". Vox.com.
- Thompson, Alex (26 July 2018). "Twitter appears to have fixed "shadow ban" of prominent Republicans like the RNC chair and Trump Jr.'s spokesman". Vice News. Retrieved 15 August 2018.
- "What Is a 'Shadow Ban,' and Is Twitter Doing It to Republican Accounts?". July 26, 2018.
- "Why Republicans Weren't The Only Ones Shadow Banned On Twitter". July 31, 2018.
- "Setting the record straight on shadow banning". Twitter. Retrieved 8 September 2018.