On my phone number, i got 2times a sigmatech master key code from VK-sigmatech and VM-sigmatech which was same as of Yahoo sent as yahoo verification code. Kindly check that how sigmtech have sent the same code. Is sigmatech has hacked Yahoo or my account or you have sent that from sigmatech. It may be possible that either Sigmatech want to hack my account or may be it has hacked my yahoo account. Kindly find it, why message of Sigmatech came on my phone on the same time when yahoo verification code came. If yahoo have not sent it through sigmatech, then block the pathway of Sigmatech or other fraudsters, so that they can not be able to block my yahoo account.