3726
In an email sent to users on 26th December , the site explained that hackers were able to conduct this breach by exploiting a known vulnerability in outdated vBulletin forum software .
 ( discover vulnerability: explained,  the site: discoverer, 26th December: time) 
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:
 ( discover vulnerability: explained,  the site: discoverer, 26th December: time) 