Comment The answer is... it depends (Score 4, Informative) 358
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An exception would be if the applicant links to his professional online presence in the CV. Then I would use that as I would any other information on the CV. However the presence on the web does not make the information different than having the same information on the CV.
If I were hiring for a sensitive position where a background check is warranted, then I would do a real background check.
But if no background check is required, why go poking around in someone's private life.