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Security researchers , beginning with Mark Russinovich in October 2005 , have described the program as functionally identical to a rootkit : a computer program used by computer hackers to conceal unauthorised activities on a computer system .
 organization: Security; person: Mark Russinovich
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
 Entities: Security, Mark Russinovich 
Answer:
 organization: Security; person: Mark Russinovich