Definitive Guide to Removing Google Analytics Spam - Analytics Edge
Sad, but true. There's a weird scene that happens when people put links into your analytics, hoping you'll click on their link and buy their stuff or pick up their malware with your browser.
This simply crowds out your real data.
I had to spend a day working this over as my Rainmaker (Wordpress) host wasn't giving me accurate data I could use. (Particularly one "traffic" spike on Dec 25 which came from no where.) But Google doesn't pay attention to your analytics for their ranking your site, so that's a relief. And the rumor has it that Google's working on closing this hole, but meanwhile...
The link above is a geeky page, but has the best data on it of the dozens of pages I looked at.
After you work this all out, the bottom line is this:
0) Don't mess with your current data. Copy that Web Site Data into a new one, where you can apply the filters you'll need to create.
1) Create second segment and test your filters in this. Very enlightening.
2) Then apply those filters to your new Web Site Data Copy. It will take some time to build this new one, as it starts from that point, so have patience (come back in a month.) Meanwhile look to that segment you set up for accurate data.
The main scene is to not freak out about the spam accounts, and never click on them. Just set up your copy of your main web data, set up your segment so you can see the real traffic now, and meanwhile build up a new data set with the filters in place.
PS. I'm reactivating this blog, so expect some new podcasts soon.