The introduction of information systems in the 20th century has significantly improved the process of business and raised modern business on an entirely different level. However, their introduction also sparked the appearance of threats to their security. One of the most infamous and dangerous of these types of threats is phishing. The term phishing refers to a type of e-mail attack that poses a threat to information system security. The e-mail typically contains a link that, when clicked on, immediately installs malware on the owner's computer, which allows the individual or organization behind this attack access to vital information. Information system security has become crucial for business processes in the modern environment. Digital security alone is no longer sufficient, and modern companies develop workplace cultures that center around information system security. The theoretical section of this paper provides an insight into the concepts of information systems, information system security, and phishing attacks. The main objective is to clarify what these attacks represent, how to detect them, and how to protect against them. The empirical section of this paper will present three isolated instances of phishing attacks and their analysis using the case study method, which will determine the similarities and consequences of these types of attacks.