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Dual purpose.
What I like most about the program is that it doesn't only stop most of the ads I've got, it also lets me effectively wipe all traces of what I've been doing on my PC. Not that I'm up to anything untoward, you understand. Of course, Firefox has an effective pop-up blocker but having these two things together has saved me a lot of unwanted hassle.
Pros: Blocks pop-ups and removes Internet history
Cons: Doesn't catch some of those annoying window pop-ups