From The Register’s “How ATM fraud nearly brought down British banking“:
And there wasn’t time for the banks to fix the problem if anyone went public with it. Their MTBU was too short. MTBU? ThatÃ¢â‚¬â„¢s Ã¢â‚¬Å“Maximum Time to Belly UpÃ¢â‚¬Â, as coined by the majestic Donn Parker of Stanford Research Institute. He found that businesses that relied on computers for the control of their cash flow fell into catastrophic collapse if those computers were unavailable or unusable for a period of time. How long? By the late 1980s it had fallen from a month to a few days. ThatÃ¢â‚¬â„¢s not a good thing; it meant that a collapse of the computers that any UK clearing bank relied on would destroy it in less than a week.