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Most of the times I have see a problem that the App Store shows an update for an app you haven't got, it's because you have a pirated app. If you have one, delete it and you will see that the update goes away.
If you have a look at the content of an app downloaded from the Mac App Store, you will see two folders: "_CodeSignature" and "_MASReceipt". Those folders contain information of the hacker's Apple ID, his/her updates at the moment he/she copied the folder to pirate the application and the apps he had installed. If you use that application in another computer, you will see the same updates as the hacker, and the problem is that you can't update it because you haven't downloaded it
Thanks Mendel for your kind reply. I had this iMAC since last year. I haven't had any problems nor installed anything new last 6 month. the only additon I made was skype a few days ago. Any idea why this update pop up now than earlier? The folders you talk about, is there a registry in the library I can look up? I have numerous apps in my computer from various sources, some friends, some internet, some purchased. Is there a way to found out which app is responsible?
If you have downloaded an app for the App Store, you can see these folders. Open Finder, go to Applications folder, right-click an app downloaded from the App Store and select "Show Package Content". Then, open Contents folder and you will see them.
I have numerous apps in my computer from various sources, some friends, some internet, some purchased. Is there a way to found out which app is responsible?
Unfortunately, it's difficult. However, you can see which applications you got from the App Store. To do it, open the System Information app (in /Applications/Utilities). Then, choose "Applications" in the sidebar, and you will see all your apps