Unfortunately there are many external threats that continually, and above all because of the Internet, end up in your PC. One of the most common are called dialers, which change the telephone number of your Internet connection for another that costs you more money, and adds profit to them.
So your PC isn`t so vulnerable to dialers, there is a tool called Omniquad Secure Dialer. It works really easily: it saves the correct number, and if there is any change or modification it alerts the user, so they don`t connect to the new fraudulent number, and can restore the real one.