-Someone screwed over by Blume and wants to bring down ctOS. Maybe an anti Aiden whose family was somehow hurt.
-A fixer working for a company rivalling Blume trying to curb the expansion while it readies its own product
-a Templar searching for a piece of Eden by kidnapping specific people for his animus and searching the ctOS. Someone has it... and he or she wants it
-A bank job. Maybe this villain is trying to learn the system, profile key employees and figure out where the money is stored. There's hacking an arm. .. then there's hacking the bank server! In the process he or she causes some havoc.
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