Get another lawyer. The owner of a trade secret has to be able to prove that s/he took appropriate steps to protect its confidentiality, in order to enforce his rights. First challenge would be defending keeping an unencrypted "secret" on an unprotected (from viruses) machine. The recipient, however, has done nothing wrong - if not a party to any confidentiality agreement, s/he has no obligation to protect the "secret" - tho the ethical thing would be to notify the infected sender.