Cryptocurrency has long been pitched as a revolutionary financial tool — but as the shocking kidnapping of NBC’s TODAY co-host Savannah Guthrie’s 84-year-old mother, Nancy Guthrie, underscores, it’s also become part of how modern criminals try to operate. Multiple ransom notes demanding payment in bitcoin — including a reported demand for around $6 million and, later, one bitcoin for information on the alleged kidnappers — have been sent to media outlets as part of the ongoing investigation into her abduction from her Arizona home. Authorities and experts continue to investigate whether the notes are credible — and whether the kidnappers are using cryptocurrency to try to obscure their identities and leverage the lack…