You are talking about what is called an "Innocent Spouse". There are two qualifications to be met. The first one is done in this scenario. One spouse has unreported income that the other had no knowledge of or reason to have knowledge of. Willful blindness doesn't work here. The second hurdle is tougher to meet and tougher to prove. The innocent spouse must be able to show they gained no financial benefit from the hidden money. Did the guilty spouse use the proceeds to buy the innocent spouse anything at all? Again, willful blindness on the part of the innocent spouse does not fly. Of course the best way to avoid current and future problems would be to file separately, but this doesn't solve past issues.