If you use Google Analytics then this bug hyper inflates all your metrics and causes you to make sub optimal marketing decisions. I was recently checking my bounce rates like every analyst does now days and was shocked when I saw my home page with an 83.95% bounce rate. It’s not a blog either it’s a B2B site offering various services which made no sense at all. Put your detective hat on and guess what, you’ve got a bug.

What it does?

In a nutshell it completely voids all your analytics data to a specific landing page and ruins your aggregate metrics bounce rate, pageviews, time on site etc.

Here’s how to find it

Three quick steps to check your GA profile

1. My home page had an 83.95% bounce rate but that doesn’t tell me much since it’s an aggregated value. Segmenting it by different channels shows that direct traffic has a 91.09% bounce rate.

2. Segment direct traffic by browser and analyse the bounce rate. (Measure it alongside contribution to visits (%) to realise “Mozilla Compatible Agent” is causing most of the high bounce rate.

3. Click on “Mozilla Compatible Agent” and view the metrics on it to realise that time on site is less than around 0, it’s all new visits and has an extremely bounce rate. Additionally a daily analysis shows a consistent pattern of visits every day (145 visits mode).

If this is evident on your analytics profile then it’s important to get rid of this ASAP.

Here’s how to get rid of the bug

In one simple step

1. Create a filter to remove “Mozilla Compatible Agent”

Go to filter manager > add filter > Name your filter > Click on “custom filter” and hit “exclude” > For Filter Field select “Visitor Browser Program” > For Filter Pattern select “mozilla compatible agent” > add it to your profile > Done!

It will probably take a day for you notice any differences and I would recommend applying any new filters to a test profile first. But obviously this has been tested out and works like a charm. (editor's note: you can also do the same action in an advanced segment and instantly see the changes without adjusting filters, and you can see changes applied to past data).

Mozilla compatible Agent is actually a valid browser do not assume its a bug until you've checked it with the above methodology.

Here’s the result after we filtered it out.

A 48.16% bounce rate is still relatively high. We can use conversion rate optimisation techniques to bring that rate down. Do check to see if your profiles have been affected by it.

What caused it?

I checked the server logs, filtered it, learnt handy excel tricks from an Excel Master and spoke to an Analytics Guru but I still couldn’t pin down the cause. It's a tricky one and if it exists on your profile I recommend removing it. Also a word of caution do not assume that Mozilla compatible Agent is a bug use the methodology above to verify it.

For all the experts out there, have you seen it before and do you know what’s causing this anomaly? A mystery surprise awaits the winner (seriously). If anyone does know the cause it would be great to share with the community.Keen to hear your thoughts.

Check out the QA discussion for extra points :)

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