There has been a new surge of referrer spam which damages data sets for Google Analytics, sometimes seriously distorting the number of sessions and page views, especially for smaller businesses.
Attackers may be doing this via bots, botnets and ghost sites, to generate traffic and sales leads, spread malware or conduct phishing attacks.
Referrer spam isn’t particularly lucrative compared to other forms of cyber-crime, but it easy and has become a real nuisance.
The attack affects a site's UA (Urchin Analytics) number, but changing this to avoid tampering will also lose the historical data needed for analytics to work. Google Analytics itself was created at a time before security became such an issue; so the advice is, if you're suspicious of your referrer data, don’t visit the sites it suggests.
Google’s John Mu has said that the company is working on general solutions.