It’s not the worldwide hacking collective Anonymous who are the most successful hackers in the world when it comes to our critical infrastructure – it’s squirrels! Critical infrastructure includes a country’s power stations, communication networks and other vital institutions. To date, human hackers have carried out just four successful cyber attacks of this kind, while the number of attacks by squirrels is at least 1,000 times that.

Despite this, criminal hackers continue to dominate the headlines even though there is little evidence of the threat they pose being put into action. That’s far from the case where squirrels are concerned, though: they carry out around 300 acts of vandalism a year in the city of Austin, Texas, alone. No one can keep count of all their attacks – or even estimate the number – because some last only a fraction of a second, causing a brief flickering of the lights at most.

Yet these tiny creatures can have a big impact – they have already shut down Wall Street’s NASDAQ stock exchange twice. In the city of Tampa, Florida, a squirrel bite led to a drinking water emergency lasting 37 hours, with residents forced to boil their water before consuming it. And in a transformer shed in Canada, a squirrel sparked a 3,000°C fireball, which cut off the electricity supply to an area the size of Britain for an hour.

Cyber defence bosses secretly admit that the four-legged hackers represent a huge problem: “The number one threat to the electricity grid is squirrels,” says John Inglis, former deputy director of the National Security Agency. But danger doesn’t just lie in the trees…

Nuclear power plants are some of the most secure facilities on Earth. To date, human hackers have caused no significant damage to them, although creatures without a brain have. In 2013, jellyfish began a mass assault that IT experts would probably call a denial-of-service (DoS) attack.

A huge swarm of cnidarians blocked the cooling water pipes of the Oskarshamn nuclear power plant on Sweden’s Baltic coast, a station that provides 10% of the country’s electricity supply. This caused one of the three reactor blocks to switch off for three days. Despite being 95% water jellyfish are a force to be reckoned with – power plants situated on the coasts of South Korea, Oman, Scotland and the US have already fallen victim to them.

Birds perched on high-voltage power lines are a common sight. And as long as they just sit there, nothing will happen. But if a stray wing were to bridge the gap between another line or mast, several 10,000-volt stationary systems will short circuit. Even small amounts of bird droppings hitting the right spot can have the same effect.

And what if the animal hackers attacked the rail network’s overhead lines? Trains would stop and the whole network would grind to a halt. A more common scenario is when a bird on a high-voltage wire catches alight after receiving an electric shock and falls to the ground: this can cause a huge fire. Meanwhile, to keep pigeons away, dummy models of their natural enemies (such as owls) can be installed. But that can lead to other problems: in at least one instance, a falcon has attacked such a fake owl, causing a power outage…

Not all ants build nests and collect leaves -the Rasberry crazy ant likes nothing more than to swarm inside electronic matter: computers, fuse boxes and even entire power stations act as a breeding ground for the three-millimetre ants’ offspring. “Perhaps because it’s warm, perhaps because they can easily defend the small spaces,” suspects Texan entomologist Roger Gold.

The ants nibble through insulation which can short-circuit electronics. If an ant is electrocuted, its body releases an alarm pheromone to communicate that they are in distress. The rest of the colony are then put into attack mode, leading to a rampage that often destroys entire electrical systems. One chemical plant saw the control system of its pipeline valves fail twice. The insects cause up to $145 million of damage per year.

Memorial Day is one of the most important holidays in the US. Thousands of military parades take place as millions of people pay their respects to the country’s fallen soldiers. Security services are on high alert as the day gives terrorists the perfect opportunity to strike at the very heart of the superpower. Back in 2013, it seemed like everyone’s worst fears had been realised.

Sleeper cells had seemingly carried out perfectly coordinated attacks: in four US states, explosions occurred at critical junctures on the electrical grid. Tens of thousands of people were affected, stuck in lifts or traffic jams. Rumours of a large-scale hacker attack quickly spread. Who was behind it? Were the Russians to blame? The Chinese? Actually, the truth is somewhat more prosaic. The perpetrators were homegrown. What’s more, they used neither computers nor explosives to carry out the attack – their weapons were their own four paws…

HOW DOES A RODENT TURN OFF THE ELECTRICITY? – Critical infrastructure – power grids, communication networks and traffic systems – forms the backbone of society. Tamper with them and civic order quickly breaks down. For years, intelligence services have discussed possible ways in which hackers could bring a country to its knees.

Governments allocate more and more resources to combat this supposed danger: “We face a cyber Pearl Harbor, a new 9/11,” warned then-US Secretary of Defence Leon Panetta in 2012. “The greatest risk is a catastrophic attack on the energy infrastructure,” General Keith Alexander, chief of the United States Cyber Command continued. “We are not prepared for that.”

What’s happened since then? Nothing. Or rather, the enemy is of a completely different kind. You see, it’s not people behind the attacks, but curious animals: birds, jellyfish, ants and, above all, squirrels. Strictly speaking, the latter are the true architects of cyber-terrorism. In some US states, every second power outage caused by an animal is down to the bushy-tailed beasts.

They were also the culprits on Memorial Day, 2013. In contrast, there have only ever been three or four proven successful attacks on industrial installations by hackers using the internet. The reason? “That kind of cyber attack is very difficult,” explains IT security expert Bruce Schneier. There’s a huge amount of programming and expenditure involved in creating a virus, which only well-equipped and well-funded secret services can afford. And even then, it takes months or years to plan.

All of which is of no consequence to the terrorist group we know as ‘Squirrels’. They don’t need money to spread their influence. In fact the group is so powerful that the Association of Energy Suppliers in the US has created its own activity log, which registers between 0.1 and 0.6 incidents per 1,000 customers every month. In California alone, these attacks cost $300 million per year.

“Typically, the animals touch current-carrying cables and a grounded component, such as a mast, at the same time, leading to a short circuit,” explains Matthew Olearczyk of the Electric Power Research Institute. Sometimes it only lasts a fraction of a second and the power supply restarts automatically. At other times the squirrel remains trapped in the short circuit position, so the system draws in more and more electricity to compensate. Subjected to temperatures of over 1,000°C, the squirrel explodes. That puts the facility out of action.

However, despite the dangers, the distributor stations still prove a huge draw for the animals. They offer shelter from predators, while the wind and cooling fans blow seeds and other foodstuffs into the installation. Plus there’s always something there for them to chew on: “A squirrel’s incisors grow 25cm per year – they have to constantly gnaw at things to wear them down,” explains University of Arizona zoologist John Koprowski.

Authorities have tried everything: bars on windows, strategically-placed dummies of pine martens, even fox urine, but nothing has stopped the creatures from hacking US infrastructure. The army of furry terrorists goes marching on…