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Specifically , as of December 2014 , the information security team understood that the attacker had exfiltrated copies of user database backup files containing the personal data of Yahoo users but it is unclear whether and to what extent such evidence of exfiltration was effectively communicated and understood outside the information security team .
 ( data breach: had exfiltrated,  the attacker: attacker, December 2014: time, copies of user database backup files: compromised data, the personal data: compromised data, Yahoo users: victim) 
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:
 ( data breach: had exfiltrated,  the attacker: attacker, December 2014: time, copies of user database backup files: compromised data, the personal data: compromised data, Yahoo users: victim) 