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Over the past few weeks , hackers have targeted thousands of publicly accessible servers running database software such as MongoDB and Hadoop , and held their data for ransom .
 ( ransom: ransom,  the past few weeks: time, hackers: attacker, servers running database software: victim, MongoDB: victim, Hadoop: victim, held their data: attack pattern) 
Locate the role in the text that participated in the event based on the event type and return it in the event list. 
 Option: Event type: phishing, data breach, ransom, discover vulnerability, patch vulnerability, Arguments type: vulnerable system, capabilities, vulnerability, number of victim, issues addressed, compromised data, damage amount, common vulnerabilities and exposures, victim, patch number, number of data, tool, discoverer, time, purpose, place, payment method, releaser, vulnerable system version, attacker, supported platform, patch, price, vulnerable system owner, trusted entity, attack pattern. 
Text: {0} 
Answer:
 ( ransom: ransom,  the past few weeks: time, hackers: attacker, servers running database software: victim, MongoDB: victim, Hadoop: victim, held their data: attack pattern) 