[header] How to distinguish between a' rogue antivirus' and a' legit' one [title] Memorize a few names of " legit " antiviruses. [step] This way you may know which is rogue and which is legit. A few legit antiviruses are mcafee, avg, avast! , norton, and kaspersky. 
Some of these are free (like avast and avg) and some of these have a trial version and a paid version (like norton or mcafee). [title] Memorize a few names of rogue antiviruses as well.