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A cybersecurity firm called MedSec initially discovered the problems in the St. Jude devices and tipped off the activist investment firm Muddy Waters , which publicized the flaws and advised clients to bet against the health care firm 's stock .
 ( discover vulnerability: initially discovered,  MedSec: discoverer, the problems: vulnerability, the St. Jude devices: vulnerable system) 
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: initially discovered,  MedSec: discoverer, the problems: vulnerability, the St. Jude devices: vulnerable system) 