If you've deliberately asked the question in this form to get broad ideas, answers like the one from Erica Friedman are good starting points.

But if you genuinely think about this issue at this level (instead of a more nuanced form, such as "how do sophisticated people manage their online personas?") then perhaps you need more experience in perception management.

In that case, yes, being open will hurt you. If your thinking is at this level, you will inevitably make a bad and costly mistake at some point. It's just a matter of time.

But if you are willing to view and develop online perception management as a skilled activity, orders of magnitude more complex than resume/portfolio creation skills, then you can get to a point where your online presence is a huge asset in any line of work, including working for the CIA and other professions where secrecy is key (I bet the people who are great at projecting a certain presence online are also great at making up great secret agent cover stories).

Start cautiously with something that's close to resumes: your LinkedIn profile, then do more with Twitter, blogging etc. as you gradually develop your skills.