The Tiny Mistake:
You're browsing the Internet one day and your antivirus software alerts you to a threat. You easily avoid it, but seconds later that AV program pings you as you trawl the Web for torrents and Ukrainian warez. Who does this "Avg" guy think he is, judging you? With the righteous fury of the scorned, you disable active alerts and forget about it.
A month later, your PC explodes and someone in Mexico steals your identity.
You'd be surprised at how many sombreros your savings account can buy.
The worst case scenario is a lot scarier when the equipment in question is controlling the power grid for a big ol' chunk of the East Coast.
On August 14, 2003, at 12:15 p.m., a systems operator in Indiana noticed a small problem with the power flow monitoring tool. Said problem provoked an annoying alarm, which the operator turned off before fixing the problem. He never turned it back on.
"I am way too hungover to deal with this shit."
Five hours later, black smoke was rising over Manhattan as the Con Ed power station there ground to a halt. Power lines were dead in Ohio. In a matter of a few hours, the problem had snowballed and stations started going offline in Ontario, New York, New Jersey and Michigan. The international connections between Canada and the United States went dead. Fifty-five million people were without power.
National Oceanographic and Atmospheric Administration
Left: The East Coast normally. Right: The East Coast after a lazy sysop.
It was the second most disastrous power outage in history, and all because of a disabled alarm. That one alarm was apparently the only alarm, because none of the other operators noticed the cascade of errors that slowly killed the power grid. Days later, the problem was traced back to a deeply buried bug that probably could have been handled without crippling eight U.S. states and a handful of Canada if someone hadn't hit "ignore warning."
On the plus side, amateur astronomers got a night of pretty kickass stargazing.
The Tiny Mistake:
If you've ever flown internationally with a smartphone, you know that the sudden change in location can make it go crazy. Your GPS stops working, the clock gives you screwy results from all sorts of time zones, the radio gives you weird error codes -- nothing disastrous.
"Honey, according to the iPhone I just invented time travel."
Things get a little more disaster-y when you scale that smartphone up into the world's most powerful fighter plane. Twelve F-22 Raptors, worth $150 million apiece, were on their way down to Okinawa. It was their first international trip and the first real test of this $66 billion project. Things went great until the squadron crossed the international date line, at which point all 12 fighters simultaneously got hit by the aircraft equivalent of the blue screen of death. Most reports just mentioned a problem with the navigation software, but it was actually a bit more serious than that. According to Major General Don Sheppard:
"At the international date line, whoops, all systems dumped, and when I say all systems, I mean all systems -- their navigation, part of their communications, their fuel systems. They were -- they could have been in real trouble."
"Um, hey, Bill -- do you remember these things having, like, guns or something?"
Imagine that you're driving cross country and all of the gauges on your car just crap right the hell out. Now imagine that scenario was 100 times worse. When a plane loses its access to fuel, speed and altitude gauges, they're basically eyeballing their way around the sky. Had the fleet hit a cloud bank, there would have been 12 parachutes blooming over the 12 most expensive cannonballs ever to splash down in a body of water.
For hours, the crown jewel of America's air force hobbled across the ocean completely helpless, and they somehow managed to make it to Okinawa safely. At no point in the design and construction of these air supremacy fighters did Lockheed Martin consider the possibility of the international date line, something that iPhones are programmed to automatically deal with.
"These won't need to go overseas, right? I think we're pretty much done with wars."