noun. 'Spam' is unsolicited online messages generally of a commercial nature, usually delivered as e-mail (i.e. virtual junk mail). Comment spam however is when someone posts off-topic commercial remarks with links in a blog's comment section.

Some comment spam is overt but just as often it takes the form of innocuous remarks such as "I agree with your article!" or "Hey, great site!" in a blog's comment section: the spammer's 'payload' being in the personal details link, which takes you to a dubious (often pornographic) site. One reason comment spam is a major problem is that if readers visit the spammer's link(s), their site often tries to install browser hijackers, tracking cookies or other adware/malware on the duped reader's computer. Most comment spam is entered by spambots rather than actually people.

Increasingly blogs are using technical means such as Turing tests, pre-publish moderation or registration in order to prevent spambots from polluting their comments sections with Viagra ads, online pharmacy scams and links to Russian porn sites.