Free: Microsoft Security Essentials or Paid: Norton Antivirus.
Frankly use your best judgement when viewing websites and downloading software. Keep your Java, Acrobat and Flash upto date. Don't install software from unknown links, enter the website address into your browser manually and select the download from there.
It's all about tricking you into installing something so be suspicious of everything.
copyright Howe Computer Services 2002
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