On my PC the "undefined" messages came from servedby.flashtalking. It arrived just after I had downloaded an update of SystemCare. This is an IObit product and I have had trouble before with this outfit so I uninstalled everything that came from them and the message disappeared on restart. But since so many of you have experienced it I was probably blaming the wrong thing.
Flashtalking seems to be a smart ad service. Probably responsible for me being repeatedly recommended tickets for England v Denmark at Wembley. I am not very interested in soccer and, if I was, I wouldn't be supporting England. Marvellous these intelligent ad targetting tools, ain't they?