A sleeper extension is a type of browser add-on or software plug-in that initially appears harmless and performs legitimate functions. However, it is designed to remain dormant or inactive for an extended period, evading detection by security software and users. At a later time, often triggered by a remote update or command, the sleeper extension activates its malicious payload, which can include spyware, adware, or other forms of malware. This technique is used by cybercriminals to bypass initial security checks and gain persistent access to victims’ systems, making sleeper extensions a significant threat in cybersecurity.