Ultimately, Windows Defender might fail to update the definitions itself for whatever reason. However, there are situations when this is not possible, such as when the PC is no longer connected to the Internet or when you haven’t been around to turn the computer on for a longer period of time. If you rely on Windows Defender to protect your computer against malware, it is advisable you run definition update on a daily basis. Unless the latest virus definitions are installed, the anti-malware tool might fail in detecting some recent threats, which could lead to data theft and a compromised system. Running any signature-based antivirus without the latest definitions might lead to serious security-related problems.
