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Ars Technica notes that security researcher Karsten Nohl demonstrated the potential impact of the flaws in SS7 last year by recording calls and tracking the location of U.S. Rep. Ted Lieu .
 ( discover vulnerability: demonstrated,  security researcher Karsten Nohl: discoverer, the flaws: vulnerability, SS7: vulnerable system, last year: 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: demonstrated,  security researcher Karsten Nohl: discoverer, the flaws: vulnerability, SS7: vulnerable system, last year: time) 