Emotet, the worlds most costly and destructive botnet, returned from a five-month hiatus on Friday with a blast of malicious spam aimed at spreading a backdoor that installs ransomware, bank-fraud trojans, and other nasty malware. The botnet sent a hefty 250,000 messages during the day, mostly to people in the U.S. and the UK. The group is known for taking long breaks and regularly taking time off during weekends and major holiday seasons.”]