Malware “Attention! Your browser is out of date! Update?”

Hello team,

Recently I discover something unusual when, as a user, visit my website, it pops up a window notification saying “Attention! Your browser is out of date! Update?” and the buttons to accept or dismiss, after clicking accept it downloads a suspicious file (my browser detects it as dangerous and blocks it).

I uploaded a backup from a week ago (the older I have) but the problem still there.

I checked out my website’s files via FTP but at first sight I couldn’t detect the “inflected” file

This is happening in all browsers I’ve checked.

Any idea where this problem can be?

Thanks.