"Thousands of executives received e-mails on Monday purporting to be federal court subpoenas but which appear to be part of a 'phishing' scam to capture sensitive data."This sounds like something that may be limited to a certain level of business and individual but it is not a good idea to underestimate the kind of people behind this kind of scam.
Indiana law does not allow for service of a subpoena via e-mail. I think the same can be said of federal subpoenas.
If you get one of these, call your attorney immediately and nothing else.