We have taken over development and maintenance of a large network of websites and moved them to a new server. One of these sites, the main account, has a problem that I am tearing my hair out over.
When you visit a non-existent page on this main site, you are shown a completely blank page. When you close the blank page, a pop-under from traffic swarm executes. This is driving me nuts because I can't figure out where this code is coming from. The .htaccess file is empty, the site is plain HTML. And the addon domains under the main domain don't experience the issue.
So what have I overloked? Where is it happening at?