ZeroFont trick makes users think that message has been scanned for threats
It's nothing new for cybercriminals to use sneaky HTML tricks in their attempt to infect computers or dupe unsuspecting recipients into clicking on phishing links. Spammers have been using a wide variety of tricks for years in an attempt to get their marketing messages past anti-spam filters and in front of human eyeballs. It's enough to make you wish that email clients didn't support HTML at all, and that every message had to be in plaintext email.