Purporting to be security experts noticing errors on your computer. State they have sent messages with no response. If you do not call 500 number they leave, your computer will be shut down permanently.
I received a call from this number on June 3, 2017 stating that they have noticed suspicious activity on my computer the past 2 weeks and to call 800-672-3809 by officer Charlie Williams in charge of Security at Headquarters for Windows to resolve issues.