A popular hypermarket chain came under criticism for failing to protect the e-mail addresses and credit card details of 50,000 customers. CloudCom Inc., a web services company, identified that the lapse was because of a worm that had breached the hypermarket’s internal servers through an unauthorized e-mail, and that the anti-malware system failed to catch the worm. Which of the following actions should CloudCom take to restrict such malwares from entering the hypermarket’s internal network?