For some time Google Analytics has been somewhat inaccurate as some of the data recorded has not been from real visitors but rather from visits to your site by “spiders” and “robots” (these are automated tools that troll websites looking for information). One particularly problematic one recently has been Semalt.com which also biases data about visitors from Brazil.
Google has now taken steps to allow users to exclude traffic from Spiders and Bots. There is a setting under Admin – View Settings which allows you to “Exclude all hits from known bots and spiders.” They are not automatically excluded until you change this setting.
The downside is that this will undoubtedly mean that your website traffic appears to drop. Nobody likes to see that! But the upside is that from now on you will have a much more accurate figure of the number of ‘real’ visitors to your site.
If you want to have more accurate stats data about real live visitors, you should change the setting, take the one off hit in your stats and accept that figures are more “honest” in future.
There is an old saying “stats, stats and lies”… Google haven’t been very upfront about this fix as they probably don’t want to admit that Google Analytics data hasn’t been as accurate as they have said it was.