If you receive a threatening letter, handle it as little as possible. Put the envelope and each page of the letter in separate see-through plastic bags. Make copies of the letter and ask the police to check the original for fingerprints. If the letter was delivered by U.S. Mail, you may also want to report the incident to your Postmaster. Don't waste your time worrying about phone taps, or imagining that strange clicks or hums or other noises indicate a tap.
Many taps are virtually impossible to detect.
Don't include your address in your telephone directory listing. Consider getting an unlisted personal number. Shred or burn confidential information. Get locking filing cabinets for your office. If someone that you do not know calls asking for a lot of information about your work or organization, take their name and number and ask to call them back.