Malicious emails work by including links or attachments that either download harmful software onto your computer or send you to websites designed to trick you into entering information like credit/debit card details or login information (called phishing).  Such emails have become increasingly sophisticated and can be sent from the mailboxes of people you know and trust or appear to come from an official source.  Once the virus, malware or ransomware gets into your computer, it can spread through your network and even send more malicious emails from your account.  All of these threats can cause serious damage to your network, cost a great deal to put right, disrupt your business and risk data breaches.