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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26th December , the site explained that hackers were able to conduct this breach by exploiting a known vulnerability in outdated vBulletin forum software .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
Please tell me event type and its trigger word from given type options. Output format is "type: trigger".  Option: phishing, data breach, ransom, discover vulnerability, patch vulnerability 
Text: {0} 
Answer:
 discover vulnerability: explained