In option B, the term "normal business functions" doesn't explicitly refer to information security incidents. It could encompass a variety of disruptions that may not necessarily involve security concerns. Option C, while focusing on the breach of availability, does not fully capture the breadth of information security incidents, which can also involve breaches of integrity and confidentiality. Therefore, option A is the most comprehensive as it covers any real or suspected adverse event related to the security of computer systems or networks, which inherently includes potential disruptions to business functions and breaches of information assets' confidentiality, integrity, and availability.