Contact the tax agency/agencies in his area. In the US, that would be Internal Revenue Service, the state tax agency, and also the county, burough, etc., and city agencies if he files taxes with them. Request that a notation be placed on their account. The IRS (US) has downloadable forms he can complete to formally advise of potential future fraud. A PIN number or other means of identifying himself on his taxes may be provided. The IRS and most state tax agencies have online sites with a wealth of information, and contact numbers. I would think that other countries have something similar.
Contact the tax agency/agencies in his area. In the US, that would be Internal Revenue Service, the state tax agency, and also the county, burough, etc., and city agencies if he files taxes with them. Request that a notation be placed on their account. The IRS (US) has downloadable forms he can complete to formally advise of potential future fraud. A PIN number or other means of identifying himself on his taxes may be provided. The IRS and most state tax agencies have online sites with a wealth of information, and contact numbers. I would think that other countries have something similar.