Dfd.pathci.net pop-ups may come up periodically or even regularly in your browser if you installed some freeware program from all kinds of suspicious online resources. There are many of such applications which users tend to download online every day. The problem is not in these utilities but rather in the fact that they are often bundled with a lot of extras like browser hijackers and especially adwares. Some of adware applications have all kinds of components responsible for display of paid ads online. The popups from dfd.pathci.net are caused by certain adware program that now resides on your system.