Advertisements provide crucial revenue for many sites. Some ads, though, are intrusive and can hijack your browsing experience. An ad blocker can neutralize the latter. However, you might want to whitelist legitimate sites with ads so that they can continue to make money on their display ads.

Some invasive web ads take the form of alerts telling you to call support for help with a system infection. You should never follow their advice, since doing so will likely put you at greater risk of paying exorbitant fees for call to premium phone numbers or clicking on links to compromised sites.