Claims they are Dell - getting warning messages about my "security" - wanted me to turn over control to them - I think not !!!!   I hung up on him.

Yep. It's a hacker scam. They convince you they are Dell or some other vendor of equipment you own. They tell you they came across security breach and offer to fix ti for you. They install software that allows them to take charge and can later grab what they want at their leisure.

He says he is from dell and that I have a warning on my computer. He knew my name, my computer brand and even my service tag #. When I checked Dell's website, this phone # was nowhere to be seen