A dialer is a program that dials your modem access number, you will find this component in certain software suites for various reasons, but you also see it in malware or viruses. If you have broadband then this is something you may not have to worry about but if you recently jumped on to the broadband wagon you may have your modem still hooked up. My advice on this situation is: if you don’t need a modem unplug and disable it.
Dialer enabled viruses are picked up just like other viruses with some sort of bait, or lure of free software or downloads. Once infected the dialer attempts to change your access numbers to some ultra high cost access numbers that are often in another country. The user may not even notice—besides a little slow down everything will seem normal, especially if you have a very fast PC. Then you get the bill! Dialers, for the most part, attempt to put a dent in your wallet, so you may have to do some explaining to get out of some absurd charge.
If you feel like you may be the victim of a dialer attack, try updating and running your antivirus software, spyware remover, and checking your access numbers to make sure everything is correct. There are of course free online scanners at Symantec and McAfee if you need a second opinion or are in-between antivirus software.
Stay safe out there,