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When two ransomware attacks hit the city of Riverside in April and May , it was n’t the first time the city ’s public safety servers lost data because of a malicious virus , this newspaper found in a review of city records .
 the city of Riverside: attacker; April: time; May: time
Given event type and trigger, please tell me the arguments of all the listed option. Output format is "name1: role1; name2: role2". 
Event type: ransom 
  Option: victim, attacker, payment method, attack pattern, damage amount, tool, time, price, place 
Text: {0} 
Answer:
 the city of Riverside: attacker; April: time; May: time