In this article, general precautions against security threats for computer network in small/medium enterprises are discussed and summarized. Discussion will also be extended beyond traditional threats onto modern new threats, and beyond traditional SMEs onto modern IoT applications. The contribution by this paper is to alert IT professionals about the potential threats which might have been under-looked by SMEs. The trends and such are inferred from big data of Google trends. In consider of the business owners being non-technical people, common explanations and proposals will be also provided in this article.