Recently I've been getting offers for mortgage protection insurance. They have the amount I borrowed printed at the bottom saying this amount was obtained from public records. How did they get this information? The offer is not from my lender. Can just anybody access my banking info? Thanks.

Mortgage loans are recorded at the courthouse with your deed.
It is either available on the intenet and/or many legal researches do routine searches and sells this info.
They will know when the ARMS are going to raise in rate , expect letters for that, if you are late in payments you will get re-finance and/or latter bankruptcy attoreny letters.

Yes, it is public information. Your social security number is really the only thing that is protected.

Some companies actually send people to the local courthouses to glean this information for their use or they sell the public information to others. This is the freedom of information of public records at work here that allows them to do this.