Spam is the colloquial name for the electronic version of unwanted communication. Unsolicited sales messages are most commonly categorized as spam, but virus-spreading emails and chain emails are also considered spam (in that they are things we would expect a spam filter to attempt to block). Compared to other forms of unwanted communication, e.g. junk mail and telemarketing, spam is more of a problem because it costs the sender next to nothing (generally less than a penny per contact, with the total cost being only loosely related to volume), while other methods cost the originator at least a few pennies per contact. It also is disproportionately costly to the receipient compared to the other methods.
In addition to email, wikis are also vulnerable to "linkspam", where a spammer (usually a 'bot) automatically posts pages of links, either overwriting existing text, adding to it, or creating a new page. This is usually not in an attempt to get anyone to actually visit the sites it is advertising, but rather to drive up their "relevance" to search engines, leading to greater traffic via those engines.
It causes problems in a number of ways, including:
- its sheer quantity often overwhelms the few genuine messages, which can then be overlooked
- even after being filtered, the few remaining spam messages can take significant time to review (to make sure they are not genuine – messages missed by spam filters are often the most genuine-looking) and delete
- spam filters can accidentally delete genuine messages
- human readers may accidentally delete or misfile genuine messages, thinking that they are spam
- accumulating spam messages, if not frequently reviewed and deleted, can overwhelm an email program's database engine and bring it to a crawl
- SPAM: request not to give in to the spammers by using prior-approval services