Spiky Direct/None Traffic

[venti]

We have noticed a large increase of (direct) / (none) traffic in Google Analytics since May 9th.

The traffic seems to be "spiky" (e.g. one day 25% of traffic, another day 10%). Most of the data points about this traffic are not present. We can say 80% come with a user agent of "Mozilla Compatible Agent" or simply "Mozilla". The bounce rate of such traffic is near 100% and the time on site is 10 to 20 seconds (could this because tracking is not working properly?). The pages hit seem to follow human usage patterns or a VERY sophisticated bot (however, we employ numerous anti-bot methods). 95% of traffic is reported as originating from the United States (our target market).

Ideas on what this might be?

[edited by: venti at 10:36 pm (utc) on May 29, 2012]

[venti]

Also noticed that this traffic DOES get reported as having clicked quite a few Adsense ads. A very high correlation, to the traffic levels. Though, the eCPM is much lower than typical traffic.

[cgrantski]

There are a lot of reasons, like ten or twelve of them, for a given visit to be recorded as direct traffic, and you'd probably benefit from reviewing them and thinking about whether any of them are likely responsible for the change.

I suspect it has to do with a site that refers traffic to you but opens your site in a new browser window, which usually means the referrer ends up being blank. Sometimes the search engines, particularly the Google Adsense program, add a new partner that treats links this way and generates a lot of traffic for your site. Or, an existing search/ad partner that already sends you a lot of traffic suddenly changes how its links work.