On Thursday I shared a laugh with a source at the expense of a mutual acquaintance: a security expert who has for the most part eschewed social networking sites. We were howling because someone who obviously knew enough about this person to push his emotional buttons had registered a Twitter account in his name and was posting some amusing but slightly mocking Tweets. The impersonated person even had several “followers” from the security community. I mention this because it raises an interesting question for people who have embraced social media, but only to a certain point: That is, does it make sense to go ahead and plant your virtual flag at various social networking sites before someone else does it for you, and potentially uses it to make fun of you — or worse — abuse your good name to trick your acquaintances into doing something harms you both? Indeed,