What is the most likely cause of excessive pop-up windows and a particular website showing in searches?

The presence of excessive pop-up windows and a specific website repeatedly appearing in searches is most commonly associated with spyware. Spyware is malicious software designed to gather information from a user's computer without their knowledge, which often results in unwanted pop-ups and redirects to certain websites as part of advertising schemes or data collection purposes.

When spyware infects a device, it can manipulate the browser's behavior, leading to the display of unwanted ads and pop-ups. This behavior occurs because spyware typically tracks browsing habits, which can then be exploited to generate revenue for cybercriminals through ad impressions or clicks. Additionally, such software can alter browser settings or the default homepage, further causing users to encounter pop-ups and redirects to specific sites.

In contrast, spam generally refers to unsolicited messages, often in the form of emails or unwanted notifications, which do not specifically cause pop-up windows in the browser environment. Viruses, while capable of causing significant harm to a system, usually manifest in other ways rather than merely producing excessive pop-ups. Social engineering refers to tactics that manipulate individuals into revealing personal information; it does not inherently involve the technical aspects of pop-up windows or search behaviors.