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Running any signature-based antivirus without the latest definitions might lead to serious security-related problems. 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.

If you rely on Windows Defender to protect your computer against malware, it is advisable you run definition update on a daily basis. 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.

Ultimately, Windows Defender might fail to update the definitions itself for whatever reason. In such cases you must either force a definition update by navigating to the designated tab of Windows Defender or by downloading and installing the latest signature definitions.

The Windows Defender Definition Updates are offline packages containing the most recent antivirus signature for Windows Defender. Once installed, they will make sure your PC is safe from the latest known viruses, spyware, PUPs, and malicious files.

It is very important that you download and install the 32-bit release for x86 systems and the 64-bit release for x64 systems. Please pay attention to the download links, since they are designed for different Windows iterations. Other than that, deployment is fast, so you will have your Windows Defender updated in minutes.