After the second squirrelcide (which downed my laboratory's primary computer system for 4 days), SRI established a cogeneration plant that was supposed to guarantee uninterruptible power, with appropriate isolation between the standby generators and the local power utility.
Source: wiktionary
each of those assumptions can be vitiated by a wide variety of circumstances -- including insider misuse, penetrations that exploit design flaws and code bugs, and other forms of subversion, as well as nontolerated failures in hardware and software, power failures, interference, acts of God, and squirrelcides.
Source: wiktionary