Iran has pledged to take revenge for the assassination of Qassem Soleimani last week
Nation state actors 'have demonstrated intent and capability to leverage VPN services… for malicious purposes'
US Department of Homeland Security directive requires federal agencies to fix critical flaws within 15 days
The countdown starts as soon as a critical flaw is detected after weekly 'cyber hygiene' scan
US Department of Homeland Security emergency order issued in response to claims of Iranian DNS hijacking attacks