Why do spyware and virus programmes downloaded from the ...

i downloaded a programme called malwarebytes and all it did was make the computer scream like a mad parrot , slow it down and make it impossible to even stop the computer, before i with great difficulty managed to uninstall the programme and get the computer back to normal

why is that?

Source: http://www.smartask.com.au/67678/why-do-spyware-and-virus-programmes-downloaded-from-the-internet-make-a-big-mess-of-your-computer

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