Clem, member of Linux Mint community posted
that the download page of Linux Mint 17.3 were hacked on 20th of February, 2016
to point to a modified Linux Mint ISO, with a backdoor in it. The hacked ISOs are hosted on 126.96.36.199 and the backdoor connects to absentvodka.com
If you downloaded Linux Mint 17.3 on 20th, Feb, 2016 then it is the hacked one.
If you doubt then you can check it using MD5 hash provided by Linux Mint team for Linux Mint 17.3.
You can find them at http://ftp.heanet.ie/pub/linuxmint.com/stable/17.3/
also along with signed sha256sums.