Porn dialers often contain malicious code
A study on current trends in "malicious code" on the Internet identifies porn "dialers" as a major problem. "These change the number used by dial up connections to expensive premium rate lines. Such programs, which are regularly modified by their creators and pose legal problems for AV firms. By adding detection for the programs (which don't load without user interaction) the vendors could be accused of restraining trade. One man's malware is another's useful utility." Not all dialers are ripoffs of this sort, but I would recommend never using them.
