Internet Censorship
Internet censorship is the denial of access to certain websites or services on the internet.
Censorship can be as local as a parent installing software on the computer their child uses to attempt to prevent them from seeing 'undesirable' content, or as global as the methods China uses to prevent a whole population from accessing content their government deems undesirable.
Both of the methods mentioned above are usually arbitrarily imposed on the audience concerned (the child in the first instance, the population in the latter.)
However, until recently, it has been assumed that in 'The West,' the public are generally allowed to view sites or use services without censorship - with a few exceptions - usually activities that are against the law 'in real life.'
For example in the UK it is illegal to access 'child pornography,' or 'terrorism' sites though there are a few anomalous areas - such as in the UK where 16 year-olds are old enough to have sex, but not old enough to be photograph each other while they do it.
More recently, however, the list of 'illegal' things to view on the internet has included things that aren't illegal in real life, such as 'extreme (adult) porn.' For example, the case of Simon Walsh, previously a barrister until the trial, who was arrested for possessing 'extreme pornography' (6 photos attached to emails; 3 of the consensual and sexual use of a urethral sound, two of anal fisting and one in which the age of a young man was in doubt[1]) was a very public and embarrassing one for Mr. Walsh, however he was acquitted of all charges.[2]
Parental Internet Controls - UK - 2012
Consultation
http://www.education.gov.uk/a00211052/parental-internet-controls
Internet Watch Foundation - Scorpions album - 5 Dec 2008
The IWF proceeded to block a single Wikipedia article covering 'Virgin Killer,' a 1976 album by the Scorpions, because it featured an unaltered image of the cover of the LP album which depicted a naked prepubescent girl. The block affected a large part of the UK's internet population[3]. The block was later rescinded with the IWF stating
the image in question is potentially in breach of the Protection of Children Act 1978. However, the IWF Board has today (9 December 2008) considered these findings and the contextual issues involved in this specific case and, in light of the length of time the image has existed and its wide availability, the decision has been taken to remove this webpage from our list.[4]
Criminal Justice and Immigration Act 2008 - Pornography - United Kingdom
http://www.legislation.gov.uk/ukpga/2008/4/section/63