REvil hackers have taken down systems of up to 1million companies worldwide
Attack began Friday after Russia-linked group infected US tech firm Kaseya
Knock-on effects have taken down IT systems of Swedish grocery stores, New Zealand schools and two Dutch tech firms - among many others
Hackers are demanding $70m in Bitcoin as President Biden tells the FBI to investigate and warns of action against Russia if it is found to be responsible
Has your firm been affected? Contact: chris.pleasance@mailonline.com