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Researchers at Trustwave are warning of a hidden backdoor in VoIP devices produced by Chinese manufacturer DBL Technology which could allow access by the manufacturer or malicious third parties .
 ( discover vulnerability: are warning,  Researchers: discoverer, a hidden backdoor: vulnerability, VoIP devices: vulnerable system, Chinese manufacturer DBL Technology: vulnerable system owner, allow access by the manufacturer or malicious third parties: capabilities, Trustwave: 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: are warning,  Researchers: discoverer, a hidden backdoor: vulnerability, VoIP devices: vulnerable system, Chinese manufacturer DBL Technology: vulnerable system owner, allow access by the manufacturer or malicious third parties: capabilities, Trustwave: discoverer) 