Security experts from Skyhigh Networks discovered a wide-scale attack with a new stealthy technique, dubbed KnockKnock, that targets Office 365 accounts. The massive campaign leverages a low-key attack, started in May and is still continuing. Attackers are using a small botnet composed of 83 IP addresses across 63 networks, most of them registered in China. The attackers targeted only a very small proportion (typically <2%) of the O365 account base, and limited the number of attempts to 3-5 per account to go undetected."] Source: https://securityaffairs.co/wordpress/63969/hacking/knockknock-attacks-0365.html