Which type of malware could be causing issues if files are disappearing and new icons are appearing without user consent?

The scenario described, where files are disappearing and new icons are appearing without user consent, suggests the presence of a type of malware that operates at a fundamental level within the operating system. A rootkit is designed to gain unauthorized access to a computer system and typically works by hiding its existence and the presence of other malicious software from the user and security software.

Rootkits can manipulate the system in such a way that they obscure the user's ability to detect unwanted changes, such as disappearing files or the creation of new, possibly malicious icons. This level of control makes it difficult for users to identify the root cause of the abnormal behavior since rootkits often maintain stealthy profiles.

In contrast, viruses tend to replicate themselves and may disrupt system functionality, but they do not necessarily hide their presence in the way rootkits do. Spyware focuses on gathering user data, often without altering the file structure or visible icons. Adware, while invasive and capable of modifying user experience by adding ads or changing icons, does not typically lead to files disappearing in the same stealthy manner as rootkits. Thus, the characteristics of the situation point clearly toward rootkits as the type of malware likely responsible for the issues being experienced.