Blogger Andy Baio was able to uncover the identities of seven anonymous bloggers from a random sample of 50 in under 30 minutes. The mistake committed by the unlucky 7 was to inadvertently link the websites where they’d chosen to be anonymous to other sites where they had not. The link was a shared Google Analytics ID; a tiny and innocuous little signature unique to each blogger but shared across all of their websites. The hard work of sifting through those billions of websites and harvesting the Analytics IDs is performed regularly by Search Engine Optimisation (SEO) tools.”]
Source: https://nakedsecurity.sophos.com/2011/11/28/basic-error-puts-anonymous-bloggers-at-risk/