Jim Hall writes "Security blogger Krebs reports that Target's data breach started with a stolen HVAC account. Last week, Target said the initial intrusion into its systems was traced back to network credentials that were stolen from a third party vendor. Sources now claim that the vendor in question was a refrigeration, heating and air conditioning subcontractor that has worked at a number of locations at Target and other top retailers. Attackers stole network credentials from Fazio Mechanical Services, then used that to gain access to Target's network. It's not immediately clear why Target would have given an HVAC company external network access, or why that access would not be cordoned off from Target's payment system network."