There are various categories of network locations that are filtered to some degree by most UK ISPs.
Each of these may be affected by various different techniques such as DPI-based blocks, DNS-based blocks, or routing based techniques.
- Child abuse imagery - usually the contents of the list produced by the IWF
- Court ordered blocks - such as those granted by Section 97A of the CDPA, see Website blocking for examples
- Adult content filters - content deemed unsuitable for under 18s
- Computer safety and security - known harmful locations may be blocked, e.g. malware sources
- Extremism - content believed to support or encourage extremism (not yet widely applied by the end of 2013)