A use of electronic messaging systems in order to send out unwanted messages in a bulk. To stop the SPAM is not a technical issue but mostly an economical one – the possible visibility in comparison to costs is still amazingly high.
The most popular spam type is e-mail SPAM, however the definition also applies to any messages sent electronically that are 100% unsolicited. The examples of SPAM are: search engine spam, comments spam, wiki spam, social media spam etc.
In majority of civilized countries SPAM is illegal. In the same time it is not so easy to catch the spammers since nowadays majority of SPAM campaigns are sent not from a single location, but from botnets, and they reside in different geo’s and networks.