Why was Rogue "Personal Internet Security 2011" not detected?

Yesterday my wife received what appeared to be a Microsoft popup warning, stating that her laptop was infected with multiple viruses and offering to remove them. As Norton Internet Security (V18.6.0.29) was installed, I suspected a hoax. The program was up to date, Live Update had occurred a few minutes earlier and a scan revealed no threats other than some Cookies.

 

However, as a second check, I did a scan using Malwarebytes and to my surprise, it picked up and quaranteened "rogue.personalinternetsecurity". Subsequent searches on Google revealed this was the 'program' that caused the supposed Microsoft message and potential threat if any of the 'fix' buttons had been clicked. This seems to be a well documented threat.

 

Since this threat is so well known, why did my Norton Internet Security apparently not identify, report and deal with this 'rogue' file?

 

Allan