Google Analytics is great for gathering data on who uses your web
application, but becomes worthless if spam sessions start infesting your
data. Here’s how we’ve tried to combat the problem for oddbird.net.
Like many websites, we use Google Analytics to gather data about our
users – what OS and browser they used, how they came to our site, etc.
But a number of months ago we started seeing lots of this:
It’s not a new problem, but it’s particularly problematic for smaller
sites that don’t receive lots of traffic. On a given day, spam hits were
accounting for anywhere from ten to ninety (!) percent of our sessions.
There are many solutions out there; since we mostly saw spam in the
“referral” field, we wanted a simple way to block spam referrals from
being included in our analytics data.
One common approach is to disallow any site visits where
document.referrer matches a known spam domain. There are free
services that create the necessary Google Analytics “filters” for you,
but they must be re-configured frequently as new spammers are added to
This approach has worked relatively well – in the first two weeks, we
only saw nine spam sessions sneak through. But we weren’t entirely
thrilled with it, either.
First of all, a disallowed-list of domains-to-block is much more difficult to
maintain than an allowed-list of domains-to-allow (even if we’ve off-loaded
most of the maintenance to the community). And second, there’s something
less-than-ideal about fetching a raw .txt file directly from someone
else’s GitHub repo, making assumptions about the format of the file
contents, and then relying on it as part of our build/deploy process.
So we’ve recently also implemented some improvements, most notably using an
allowed-list filter to exclude any hostnames we haven’t explicitly authorized.
This takes care of most of the spam, and is arguably cleaner and easier to
We haven’t been using this technique for long, but so far the results
have been positive. If it continues to work well, we’ll likely remove
the referral-blocking code entirely.
If you use Google Analytics, how have you tackled the problem of spam
infecting your data? Let us know via Twitter!