"They Loved Your GPA, Then They Saw Your Tweets"

In this article they talk about how when applying for college they can look at what you post on social media. I was surprised when I read that "As certain high schools seniors work meticulously this month to finish their early applications to colleges, some may not realize that comments they casually make online could negatively affect their prospects." Meaning that the things that they say or post on social media can affect their chance of being excepted into college. I was wondering if your account is private, if they still have access to look over them? I don't really put bad things online however when the time comes closer to apply for college, I will definitely review my account and just be more cautious as to what I choose to post online.