In the Cyberpunk subgenre of science fiction, and in Shadowrun specifically, IC is short for Intrusion Countermeasures, and is pronounced (And usually written) as "ice."

IC is used to defend a system from attacks by hackers (Deckers, in Shadowrun and some other places) . There are many different kinds of IC, but they are usually broken down into three categories:

  • White Ice: Totally benign defenses, such as firewalls and alarms.
  • Grey Ice: Mildly harmful countermeasures, designed to nullify a hacker's intrusive abilities, by damaging or destroying his programs, and possibly his computer.
  • Black Ice: Very harmful countermeasures, designed to physically harm or even kill the hacker. Although these are usually illegal, many megacorporations use Black Ice to defend high-security data and facilities.