Multi-factor authentication can prevent accounts from being accessed if passwords are stolen or obtained using brute force tactics; however, Proofpoint has discovered that multi-factor authentication is being bypassed on Office 365 and G Suite accounts using the legacy IMAP protocol. The IMAP authentication protocol bypasses MFA and attackers are able to avoid being locked out of accounts. The methods used made failed login attempts appear like isolated fails, so they are not detected. Attacks are conducted using a network of thousands of hijacked devices such as vulnerable routers and servers with...