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The Internet is a polluted place, infested by viruses and over-populated by unsolicited junk such as spam and popups. While in theory there exist all the tools we need to protect ourselves from these nuisances and risks, in practice it is impossible for most casual users and for many companies to steer clear of them. Software vendors, notably Microsoft, are culpable of failing to provide sufficiently transparent and user-friendly protection, with vulnerability continuing to be the default option.
Philip Hunter (Sun,) studied this question.