Locky, a massive ransomware campaign that made headlines last month, sent out more than 27 million phishing emails during a 24-hour period earlier this week. It's one of the largest malware campaigns so far this year, cybersecurity experts say. A majority of the attacks originated from Vietnam, while others came from India, Columbia, Turkey and Greece, according to Campbell, California-based cybersecurity firm Barracuda Networks. The emails took on several different forms - some impersonated 'copier' file deliveries, emails from nutrition brand Herbalife, or fraudulent invoices from Amazon Marketplace. All contained ZIP files with Locky hidden inside. If recipients clicked on them, the ransomware downloaded to their computers, encrypting and freezing all files. Then, they're asked to pay for a special type of software that restores the locked files.Locky, which surfaced in February 2016, usually demands that users pay ransoms via Bitcoin, which can keep transactions hidden from authorities. The ransomware has the potential to pull in big money for hackers, even if only a few people fall victim to the emails. Unfortunately, cybersecurity experts haven't developed a way to unlock impacted files without having to pay ransom.Locky is one of the most prominent types of ransomware and was one of the most common varieties of malware used by cybercriminals last year.