UPDATE July 2015: This is a never-ending topic. For the latest ideas, we recommend you read this article on the Moz blog instead.
When you look at the “referring sites” report in your visitor analytics application, you may find some intriguing referrers. Why would some particular sites refer to you? I’ve written before about how you can use Google Analytics to backtrack and find the actual page on their site which is linking to you. However, some sites apparently linking to you are unwanted. They’re just firing some code at your site which makes your analytics application think you’ve just received a visitor from their site. This is called “referrer spam”, and it can seriously distort your website visitor traffic figures.
You can tell referrer spam by the fact that a site apparently sends a lot of visitors, but almost none of them register as staying on the site. The bounce rate will be close to 100% – as will the percentage which are classed as “new users”, as your analytics application can’t tag them as having visited before. And they can send a lot of visitors, as this example shows:
Actually blocking these visits is possible, and you might want to discuss it with your website hosting company, but it’s quite a technical process. Somewhat easier is just filtering them out of your analytics reports. I’ve discussed how to filter out referrer spam – such as “Semalt” – here and how to switch on Google Analytics’ robot filtering here. Note, however, that neither technique will get rid of historical visit data; you’ll need to filter the reports themselves to do that.
Unfortunately, it’s a never-ending job. If something curious crops up in your referring websites report, and you discover it’s just referrer spam, you’re going to have to add it to the filters, as described above. Those of you who’ve successfully eliminated “semalt”, for example, might now find “buttons-for-website” appearing. We’d all like the analytics application providers to spot these and eliminate them on our behalf, but it seems that this is a task they don’t fancy.
For those of you who are wondering why somebody goes to the effort of setting up referrer spam, I believe it’s all about linking. Many websites publish “top ten” tables of the sites which send most visitors to them. These tables are usually created automatically, and the sites listed in the table get a link back, as some sort of a thank-you. So unscrupulous website owners have devised ways of forcing their sites to the top of the referrer statistics on millions of websites, getting a handful of links in the process, sometimes from decent sites. Whether these links are any use in Google is questionable, but it’s not going to stop people trying it.
In the meantime, here’s that article again on how to filter out referral spam from Google Analytics.