In recent years, cyber a acks have caused substantial nancial losses and been able to stop fundamental public services. Among the serious a acks, Advanced Persistent reat (APT) has emerged as a big challenge to the cyber security hi ing selected companies and organisations. e main objectives of APT are data ex ltration and intelligence appropriation. As part of the APT life cycle, an a acker creates a Point of Entry (PoE) to the target network. is is usually achieved by installing malware on the targeted machine to leave a back-door open for future access. A common technique employed to breach into the network, which involves the use of social engineering, is the spear phishing email. ese phishing emails may contain disguised executable les. is paper presents the disguised executable le detection (DeFD) module, which aims at detecting disguised exe les transferred over the network connections. e detection is based on a comparison between the MIME type of the transferred le and the le name extension. is module was experimentally evaluated and the results show a successful detection of disguised executable les.