There was an article about them in The Guardian a while back.
According to that, they are based in India at a call centre. Although the methods they use are immoral and potentially dangerous, the article suggested that this particular organisation has become so prolific by staying (just) within the law. What they are 'selling' is a service which mostly consists of installing freely available software that the user could have downloaded for free at any time.
Usually, when a forum gets going against them, one or more 'satisfied customers' come on singing their praises.
My advice is to ignore them, or you could try telling them that you don't have a computer, or you use a Mac.