Msmpeng.exe is a legitimate and essential component of Windows Defender, Microsoft's built-in antivirus and anti-malware software. It stands for Microsoft Malware Protection Engine and plays a crucial role in protecting your computer from various threats, such as viruses, spyware, and other malicious software. While Msmpeng.exe is an essential part of Windows Defender's protection mechanism, it can sometimes consume a significant amount of CPU resources during system scans or updates, leading to temporary performance slowdowns. However, this behavior is normal and expected during intense scanning activities and usually shouldn't cause major issues. At the same time, malicious programs, like Trojans, Spyware, and Rootkits, may attempt to masquerade as the legitimate Msmpeng.exe process to avoid detection and remain undetected on your computer for extended periods. So you should be aware of this potential threat and use reliable security software to protect your system.