This invention relates to screening of spoken audio data so as to detect threat words or phrases. The method is particularly useful for protecting children or vulnerable adults from unsuitable content and/or suspicious or threatening contact with others via a communication medium. The method is applicable to screening speech transmitted over a computer network such as the internet and provides screening of access to stored content, e.g. audio or multimedia data files, as well as real time speech such as live broadcasts or communication via voice over IP or similar communication protocols. The method allows an administrator, e.g. a parent, to identify groups of threat words or phrases to be monitored, to set user access levels and to determine appropriate responses when threat words or phrases are detected.