No offence for comparaison to condoms.
Thanks to your many replys.
I mostly agrea with all of you and think we don't control user's behavior, despite any education we can give and even if they try.
At risk or not, users are victims of viruses and making them fell guilty doesn't help.
In the case of my customer, she receives a lots of emails daily and says she is never opening one she was not expecting.
I however beleive she opened one from DHL (which I already identifyed long time ago as a vehicule for virus) or from someone else, as she was expecting some data from them.
She only realized Lukitus virus inpact 2 days later, when looking for a file.
I wouldn't even qualify her at risk, but as a real victim.
I found this very interresting post on ESET forum : https://forum.eset.com/topic/1714-eset-and-malwarebytes-comparison/
and I think I will have to purchase Malwarebytes along with ESET.
Thanks again, and sorry for my poor english