UPDATE July 2015: This is a never-ending topic. For the latest ideas, we recommend you read this article on the Moz blog instead.
An update today on the “spambots” problem which has been causing such heartache to serious users of Google Analytics. If you’re using BMON to manage your Google Ads, we’ll have tried to keep on top of this for you, but for those of you managing things on your own, have a read of How to Stop Spam Bots from Ruining Your Analytics Referral Data on The Moz Blog. The article is a good update on its own, but really gets going if you start to read the comments. Here, various webmasters have weighed in, including one or two who’ve discovered that some of these “spambots” never actually visit your site at all. I don’t think many people saw that coming.
There are some solutions suggested which might be worth a go if you’re comfortable with setting up blocking at the server level, but these won’t overcome the problem of the spambots which never actually visit your site. For that, you’ll need to use filters in Google Analytics, and for historical data, use segments. We are already starting to implement spambot-ignoring segments for our Google AdWords reporting.