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One of the largest trading posts on the Dark Web , AlphaBay , has rewarded a researcher for disclosing the existence of a vulnerability which allowed him to steal over 200,000 private messages exchanged between users and sellers .
 ( discover vulnerability: disclosing,  the existence of a vulnerability: vulnerability, a researcher: discoverer) 
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: disclosing,  the existence of a vulnerability: vulnerability, a researcher: discoverer) 