- Illegal use of licensed radio spectrum (also known as bootlegging in CB circles) is fairly common and takes several forms. Unlicensed operation—Particularly associated with amateur radio and licensed personal communication services such as GMRS, this refers to use of radio equipment on a section of spectrum for which the equipment is designed but on which the user is not licensed to operate (most such operators are informally known as "bubble pack pirates" from the sealed plastic retail packaging common to such walkie-talkies). While piracy on the US GMRS band, for example, is widespread (some estimates have the number of total GMRS users outstripping the number of licensed users by several orders of magnitude), such use is generally disciplined only in cases where the pirate's activity interferes with a licensee. A notable case is that of former United States amateur operator Jack Gerritsen operating under the revoked call sign KG6IRO who was successfully prosecuted by the FCC for unlicensed operation and malicious interference. A subcategory of this is free banding, the use of allocations nearby a legal allocation, most typically the 27 MHz Citizen's Band using modified or purpose-built gear.
- Inadvertent interference—Common when personal communications gear is brought into countries where it is not certified to operate. Such interference results from clashing frequency allocations, and occasionally requires wholesale reallocation of an existing band due to an insurmountable interference problem; for example, the 2004 approval in Canada of the unlicensed use of the United States General Mobile Radio Service frequencies due to interference from users of FRS/GMRS radios from the United States, where Industry Canada had to transfer a number of licensed users on the GMRS frequencies to unoccupied channels to accommodate the expanded service.
- Deliberate or malicious interference—refers to the use of two-way radio to harass or jam other users of a channel. Such behaviour is widely prosecuted, especially when it interferes with mission-critical services such as aviation radio or marine VHF radio.
- Illegal equipment—This refers to the use of illegally modified equipment or equipment not certified for a particular band. Such equipment includes illegal linear amplifiers for CB radio, antenna or circuit modifications on walkie-talkies, the use of "export" radios for free banding, or the use of amateur radios on unlicensed bands that amateur gear is not certified for. The use of marine VHF radio gear for inland mobile radio operations is common in some countries, with enforcement difficult since marine VHF is generally the province of maritime authorities.