A dialer (or dialler) is a computer program which creates a connection to the Internet or another computer network over the analog telephone number. Usually it’s  a number beginning with 0-700 (in Poland)  or the foreign telephone number. Usually,  dialer is working without  user knowledge. The dialers which appear the most frequently on the pornography pages are harmful only for modem users.

Dialers are necessary to connect to the internet (at least for non-broadband connections), but some of them are designed to connect to premium-rate numbers. The providers of such dialers often search for security defect on the user’s computer and use them to change the computer to dial up through their number, pocketing the additional money for themselves.

Alternatively, some dialers inform the user what are they doing, with the promise of special content, accessible only via the special number. Examples of this content include software for download, MP3s (usually illegal), pornography, and in the case of at least one website, ‘underground’ hacking materials such as viruses

Nowadays, the term “dialer” often refers specifically to dialers which connect without the user’s full knowledge of the costs, with the creator of the dialer intending to commit fraud.