How to remove unwanted files from imac

I stupidly downloaded a supposed anti virus program which turned out malicious, producing unwanted popups.
I have tried to remove it by dragging it to trash but it tells me it can't be trashed because the program is still open.
What to do?!!
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nappy_dThere are a 1000 ways to skin the technology cat.Commented:
Reboot your computer in safe boot mode. This is done by holding down the left shift key at startup.

Keep holding the shift key till you see the text "safe boot".

Now, remove the app.
Close the application:

Then you can delete it.
HSumlinAuthor Commented:
Doesn't work!! When I open the Force Quit window the offending program doesn't appear. So it can't be deleted.
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HSumlinAuthor Commented:
Can someone help me with this please!
First check System Prefs/Accounts/Login Items and remove any software that you don't want starting at start up. Then restart holding down the shift key (safe boot).

Also google the term remove <malware> if you know the name of the product you installed.

Let us know if any of this helps and then we can take it to the next step.
What is the name of the software that you installed?
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