I thought when we sign our apps, we are accepting the possibility that our info will be checked. I presume this would include salary info as well.
It does in theory, but giving the school authorization to call your employers does not give your employers authorization to disclose data about you to the school. Generally speaking, all that most employers will disclose are: Dates of employment, title, and occassionaly whether or not you are eligible for rehire. Salary is typically NOT disclosed. Don't take that as an invitation to lie of course. Policies vary by company, but generally speaking they are very very restricted as to what they can and cannot disclose. Too many lawsuits.
I remember one time where a kid came in and interviewed with my firm. Someone knew someone from his current job and put in a call to find out how good he was. Word gets out, and the kid's manager fires him. We didn't make him an offer. He threatens to sue us, becuase he never gave us permission to call his employer (in fact, he explicitly said no) and we did anyway - costing him his job. I don't know how the story ended, but you get the idea.