This week I received four missed calls from "DELL TECH SVC, 1-877-790-3355.  They had left no messages.  The fifth time, I answered and a fellow [from an extremely noisy boiler-room with a lot of static and frequent cut-outs] said that he worked for Dell and was calling about error messages that Dell had received from my computer.  
He had the Service Tab Number of my computer and said that I may have downloaded malware on August 18, which is when they started receiving error messages.
He showed me how to start the Event Viewer on my computer and walked me through displaying a Windows application log.  The log showed 903 errors and warnings, which he said was terrible but that he could fix the problem.  My suspicions and the noisy connection finally wore me down and I hung up.

I called the number from the caller ID, and was told that they were the real Dell Tech and the other call was bogus.