On the Internet, a block or ban is a technical measure intended to restrict access to information or resources. Blocking and its inverse, unblocking, may be implemented by the owners of computers using software.  Some countries, including China and Singapore, block access to certain news information.  In the United States, the Children's Internet Protection Act requires schools receiving federal funded discount rates for Internet access to install filter software that blocks obscene content, pornography, and, where applicable, content "harmful to minors". 
Blocking may also refer to denying access to a web server based on the IP address of the client machine.  In certain websites, including social networks such as Facebook or editable databases like Wikimedia projects and other wikis, users can apply blocks (based in either IP number or account) on other users deemed undesirable to prevent them from performing certain actions. Blocks of this kind may occur for several reasons and produce different effects: in social networks, users can unrestrictedly block other users, typically by preventing them from sending messages or viewing the blocker's information or profile. Privileged users can apply blocks that affect the access of the undesirables to the entire website.
Blocking is used by moderators and administrators of social media and forums to deny access to users that have broken their rules and will likely do so again, in order to ensure a peaceful and orderly discussion place. Common reasons for blocking are spamming, trolling, and flaming. Some criticize cases of the use of bans by administrators of large websites, such as Twitter,  saying that these bans may be politically or financially motivated. However, websites have a legal right to decide who is allowed to post, and users often respond by "voting with their feet" and going to a place where the administrators see their behavior as acceptable.
Blocked users may be completely unable to access all or part of a site's content, which is usually the case when censoring or filtering mechanisms are responsible for the block. Under a stealth ban, a user is given the false impression that their content is still being posted to the site, when in reality it is being hidden from all other users.
Ban evasion is the act of attempting to get around a ban, whether temporary or permanent, on a website.
Alternate accounts set up by people evading bans from websites are referred to as sockpuppets. Typically, if someone is caught evading a ban with a sockpuppet, the sockpuppet account is banned. If the original ban was temporary, it may be extended or even made permanent. Sometimes, the user's IP address may be banned as well so the user cannot access the site or create new accounts. Some sites may remove all but a few traces of the ban-evader. TV Tropes and Wikipedia, for example, may mass-delete any pages created by a ban-evader.
Ban evasion can be detected by tracing a user's IP address. If two accounts are using the same IP address, it could be a sign of ban evasion. Also, the use of a VPN, shown by rapid, drastic changes of IP address by the same user in a short period of time, can also be a sign that the user was trying to get around a ban. Ban evasion can also be spotted if posts or other contributions from two accounts look the same or similar, or on sites where the same email can be associated with multiple accounts, identical or similar emails can be a sign of ban evasion. Users who have been permanently banned for ban evasion may not be able to appeal their ban, which is the case on sites such as TV Tropes. 
When creating sockpuppets, ban evaders use a variety of tactics to disguise the fact that the new account was created by a previously banned user, such as using new names, an alternate email address, VPNs or proxy servers to mask their IP address, changing their IP address (sometimes only needing to rely on a dynamic IP address to automatically change it after a time), or using the site from public Internet access locations such as schools and libraries.
- Westfall, Joseph (2012). "Internet Blocking". Retrieved 25 November 2016.
- "Children's Internet Protection Act | FCC.gov". fcc.gov. 2012. Retrieved 17 June 2012.
- "Access Control - Apache HTTP Server". httpd.apache.org. 2012. Retrieved 18 June 2012.
- "Twitter bans conservative writer Milo Yiannopoulos for good, while cracking down on abuse". 2016. Retrieved 15 Feb 2017.
- "What to Do If You Are Suspended / Administrivia". Tvtropes.org. Retrieved 12 November 2017.
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