I must admit i was surprised by #3. I have used Irfanview myself on my own computers for years with never a problem. On top of that I have installed on a quite a few other computers for people over the years and also no problems. A the moment I have it installed on my desktop running Win 7, an old Toshiba running XP, my laptop also Win 7 and on my wife's laptop, Win 8.1.
Where did you download it from ? The official web-site points you at CNET for the download and I have never had a problem downloading from there but it does pay to look carefully at all the install screens when installing any software downloaded from the internet.
Could this be a false positive ?