Beware - appears to be an IRS scam.
Got a call on my answering machine from "Officer" Michael Delgado of the IRS Crimes DIvision (202-239-7249). The message was that some serious criminal complaints have been made against me and I need to call him back immediately before they proceed with criminal charges. Having had a few minor disagreements with the IRS, I know they contact in writing through the mail first. I was suspicious so I checked the phone number and found a forum and a couple Twitter posts about the IRS scam. I haven't decided if I will just blow it off or call him back and demand information in writing.