Google Analytics is showing a spike in your Direct traffic. Your offline website marketing efforts must really be taking off, right? Direct traffic means people are either typing your URL directly into the address bar or they’ve bookmarked the link straight to your page, right? Well… maybe not so much.

GA divides traffic into 4 categories: Referrals (from other web sites); Organic (from search results that arise from using great SEO strategies); Paid (from your Search Engine Marketing campaigns); and Direct (the result of the actions described above).

That, however, isn’t exactly how it works. Direct traffic – that surprisingly high number that evades your intuitive sense of reality – actually includes not only visitors that type your URL directly into their browsers or use bookmarked links. It also includes all other traffic that can’t be identified in any of the other three categories.

How much traffic falls into this “unidentifiable” category?

As reported in SearchEngineLand, an experiment by Groupon showed that up to 60% of web site traffic recorded as “direct” was actually from indeterminate sources. There are many reasons this could be the case.

First, the HTTP tech spec doesn’t permit referrals to be recorded when a visitor is coming to your “http://” web site address from a secure page (a page using Transport Layer Security or “https://”). In addition, more people are using browser plugins that strip off the referrer information, as do some devices other than desktop browsers. Even traffic from some mobile apps isn’t marked as “direct.”

Hopefully, you’re already tagging your online campaigns with Google’s Campaign URL Builder. This can help you get a handle on where visitors come from when they click on those links no matter how they click on them.