"Programs that use a system, without your permission or knowledge, to dial out through the Internet to a 900 number or FTP site, typically to accrue charges."
A dialer sets up a type of VPN(Virtual private network), which in MOST cases isn't a good thing, but the technology itself isn't horrible, just the implementation.
i spoke to a lady on the phone the other day who had a dialer on her machine and it was charging her 16 dollars a minute as it had been using an access number in australia. She was mighty, mighty pissed!
Dialers
Software that gets installed on your computer that has the ability to make phone calls from your computer, if you have a modem, without your knowledge. These programs will connect to other computers, through your phone line, which are usually porn sites. These numbers are pay per call though, so you get charged for the amount of time your computer is
connected to it.
Check this out. Nice bit of information. http://www.bleepingcomputer.com/forums/index.php?showtutorial=41