This is driving me mad frankly. I discovered an iFrame (see above screenshot) deleted flushed the cache a billion times but the link still lands on: http://www.affiliatewindow.com/closedmerchant.php?mid=2829&aid=271445
If anyone want to stop me from setting my head on fire please ping back a possible fix
Yes, it sounds like a virus on the host server, probably from an insecure script not necessarily from your site.
Check your hosts server is up to date and virus free.
Then change all your ftp and host login password etc and also run a full virus scan on your local computer. It may be you have a virus on your own computer that attaches itself while you upload via ftp.
The virus/script may be browser selective (attaches to a vulnerability in certain browsers) which is why maybe all will not see it.
If you google “site hacked with iframe” you will get a load of suggestions as to what might be the cause.
I have since resolved the affiliate link problem. The screen shot below shows the script that was getting fired everytime the hyperlink was clicked on. We removed the code and hey presto lins behave normally now!