Tags and which ppc they are coming from

[jremsen]

Hi

I have noticed that people are using tags at the end of there url like this ?ref=7s this is to know where the traffic is coming from. Now ?ref=7s is coming from 7 search and is networks , that much i know or ?ref=ma is coming from mamma and its networks , but where and what is this from ?ref=mv witch search engine is mv??