What does reference code 1541 mean on a processing delay at the IRS?

I got this code on the "where is my refund" on IRS.GOV when I checked to see what date I should expect my return. I had already had my refund "Accepted" according to Turbo Tax but when I checked this am it said there has been a delay and to call the IRS and give reference code 1541.

I called IRS and they are saying I am having my refund looked into for alleged unreported income from 2011. They didn't say much else except they will be in touch. I would assume if you get this code you are being looked into for one reason or another. Hope this helps.