It is well known that sources that threaten the data privacy of economic subjects through human interference, no matter if it is accidental or on purpose, could be divided into: inner, outer, and combined sources. As outer sources of threatening are considered persons, who are not employed in the economic subject, but whose damaging behavior could influence negatively on the subject's safety. To this group are also classified the companies that are in charge of private security, including detective agencies as well. While working on assignments in their scope of work, these safety subjects come regularly to the data, which are regarded as a business secret and should not be published. All the collected data and knowledge during their investigation work could only be used for the original purpose and at the end of the investigation should be handed over to the client (except for the ones, which are not considered as significant for the job and which should be destroyed in a certain period of time). When keeping the business secret, a company or an agency is obligated to abide by the regulations for personal data protection, no matter if the data analysis is done automatic, half-automatic, or in some other way. If subjects of private security have a need to use personal data, this is allowed only under conditions, which are regulated by the laws in this scope of work, or with clients' consent. As for the determination of secret data, it is important to differentiate the public from secret ones and to respect public principles for the simultaneous protection of the society and the state. Additionally, a business secret should be differentiated from the professional one, as well as business intelligence from business espionage.