Many website owners rely diligently on the accuracy of Google Analytics for site statistics.
Previously Analytics has arguably been more accurate than other statistics packages because Google said that it did not record visits from Robots, Crawlers and Spiders indexing your site (these are not real visitors but automated tools).
A number of months ago many of us in the SEO / Web marketing business noted increased visits from Brazil. This turned out to be visits from a Robot called Semalt.