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The article , citing research by Tobias Boelter , a cryptography and security researcher , accused WhatsApp of having a backdoor that it or Facebook could use to eavesdrop on user messages .
 ( discover vulnerability: accused,  WhatsApp: vulnerable system, a backdoor: vulnerability, Tobias Boelter: discoverer, eavesdrop on user messages: capabilities, Facebook: vulnerable system owner, cryptography and security 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: accused,  WhatsApp: vulnerable system, a backdoor: vulnerability, Tobias Boelter: discoverer, eavesdrop on user messages: capabilities, Facebook: vulnerable system owner, cryptography and security researcher: discoverer) 