Information systems are frequently exposed to various types of threats which can cause different types of damages that might lead to significant financial losses. Information security damages can range from small losses to entire information system destruction. The effects of various threats vary considerably: some affect the confidentiality or integrity of data while others affect the availability of a system. Currently, organizations are struggling to understand what the threats to their information assets are and how to obtain the necessary means to combat them which continues to pose a challenge. To improve our understanding of security threats, we propose a security threat classification model which allows us to study the threats class impact instead of a threat impact as a threat varies over time. This paper addresses different criteria of information system security risks classification and gives a review of most threats classification models. We define a hybrid model for information system security threat classification in order to propose a classification architecture that supports all threat classification principles and helps organizations implement their information security strategies.