Likely Windows Security scam. Said he was from Telstra in Sydney and gave his name as Martin Wilson, an excellent Asian name. He took me step-by-step, as published elsewhere on the web, through Windows-R through config.sys and thereafter into eventvwr where he pointed out all the errors my computer had. This indicated I needed to update my windows encryption. He wanted me to update through syskey that opened up the SAM Lock tool, at which stage I became very defensive and he ended the call without even saying farewell and thank you. :)