Microsoft Office 365’s Safe Links are designed to protect users from malware and phishing attacks. However, attackers have been using zero-width spaces (ZWSPs) to bypass security features of Office 365. ZWSP characters are non-printing Unicode characters that typically used to enable line wrapping in long words, and most applications treat them as regular space, even though it is not visible to the eye. The Z-WASP attack is another chain in a list of exploits designed to obfuscate malicious content and confuse Office 365 security.
Source: https://thehackernews.com/2019/01/phishing-zero-width-spaces.html