microsoft-security-system.xyz pop-up generated by some kind of adware or potentially unwanted program can cause distress and then help promote some kind of tech support service. This alert may disguise itself as warning page from Microsoft with blue or red background. Or it may resemble the layout of BSOD, which computers display when a system error occurs. Being a sufferer, you may be warned by a fake scan result of virus infection and urged to call 1-844-645-4279 for support.