Online information divides roughly into 3 categories:
What I advertise to prospective employers (e.g. StackOverflow, Xing, LinkedIn)
What is available about me under my real name, but isn't specifically advertised to employers (e.g. a blog, Twitter or public Facebook information)
What I post "anonymously" or intentionally kept private (Disqus posts, Twitter or facebook under false names, posts on other bulletin boards, restricted Facebook profile content).
Obviously, the first 2 categories are stuff that I'm aware potential employers can see. The 3rd category isn't - it consists of the kind of personal stuff that I don't usually advertise in the workplace.
I should make it clear, that I'm not hiding any terrible secrets like membership of terrorist organisations, extreme political views, or even embarrassing drunken photos. Neither am I applying for government jobs where I would expect to be vetted. This question is really about how separate should we expect private life and professional life to be in 2015.
What information do HR routinely have access to about professional candidates in the EU (maybe also things that I haven't thought of mentioning)?
For example, can they see information collected online by companies like Disqus about the sort of articles that people post on under a username, and would they have access to twitter or facebook accounts that are under "anonymous" usernames?