Note that many websites have their own advertising, unrelated to adware.
A type of software typically used by pornographic vendors. Once dialer software is downloaded the user is disconnected from their modem?s usual Internet service provider and another phone number and the user is billed. While dialers do not spy on users they are malevolent in nature and can rack up expensive and unwanted bills.
Some dialers are used for "legit" purposes, meaning that a user knowningly accepts the charges in exchange for some "online content". But many times we have seen dialers used in sneaky ways, using various tricks to get it installed on a users machine, without them knowing what it going on.
In general, if a dialer is detected on your system, you either know why and how it got there or it sneaked in illegally