In all cases listed above, including both commercial and non-commercial, « spam happens » due to a positive Cost-benefit analysis result.
Cost is the combination of
Overhead: The costs and overhead of electronic spamming include bandwidth, developing or acquiring an email/wiki/blog spam tool, taking over or acquiring a host/zombie, etc.
Transaction cost: The incremental cost of contacting each additional recipient [...]
The European Union’s Internal Market Commission estimated in 2001 that « junk e-mail » cost Internet users €10 billion per year worldwide. [16]
The California legislature found that spam cost United States organizations alone more than $10 billion in 2004, including lost productivity and the additional equipment, software, and manpower needed to combat the problem.[17]
Spam’s direct effects include [...]
Spamming has also been used as a denial of service (« DoS ») tactic, particularly on Usenet. By overwhelming the readers of a newsgroup with an inordinate number of nonsense messages, legitimate messages and computing resources can be lost in the deluge. Since these messages are usually forged (that is, sent falsely under regular posters’ names) this [...]
E-mail and other forms of spamming have been used for purposes other than advertisements. Many early Usenet spams were religious or political. Serdar Argic, for instance, spammed Usenet with historical revisionist screeds. A number of evangelists have spammed Usenet and e-mail media with preaching messages. A growing number of criminals are also using spam to [...]
Main article: Newsgroup spam
Main article: Forum spam
Mobile phone spam
Main article: Mobile phone spam
Mobile phone spam is directed at the text messaging service of a mobile phone. This can be especially irritating to customers not only for the inconvenience but also because of the fee they may be charged per text message received in some markets. [...]