In Weapons for a civilisation-destroying giant robot I asked about what weapons might be placed on a sixty-billion-ton fusion-powered snakebot 9.27 km long and 1.19 km in diameter, armoured with 224 metres of Boron-Carbide surfaced Tungsten-Depleted Uranium alloy armour.
The snakebot is equipped with a multitude of sensors on its skin, including optical sensors from the far UV to the far IR, electromagnetic sensors, audio sensors (for what it matters given that it would most likely have to stop moving to hear anything) and radiological sensors. It also has broad-band radar and lidar capabilities. While these sensors are surface-mounted, they may be retracted for defensive purposes (and to protect them if the snakebot rolls), and replacements are available further beneath the armour in case of battle damage.
The snakebot is armed with hundreds of "small" railguns dispersed over its outer armour, each firing a steel optically-self-guided flechette about 18mm in diameter and 288mm long at velocities of around 5000 metres per second, at around two rounds per second.
It is also armed with six large railguns in its "mouth", only one of which is available for use at any time, the others being retained deeper beneath the mouth's armour as immediate-use backups, firing 144mm diameter, 2304mm long optically-self-guided munitions at a velocity of around 7000 metres per second, at about 40 rounds per minute. These munitions may be single depleted-uranium long-rod penetrators, or they may be capable of breaking up into hundreds of unguided steel sub munitions at some point prior to impact.
Resupply of these munitions (except for the depleted uranium munitions, which would be used sparingly) would be by the expedient of the snakebot "eating" ferrous human infrastructure and processing it into more ammunition.
The snakebot is supported by a multitude of nanite-controlled birds which act as its spies. The controlled birds act naturally as far as possible, and each bird stays within its species' natural range. They will not attack and neither will they defend themselves from attack beyond those defences typically used by their species.
Prior to commencement of the attack, the snakebot's nanites have also tapped into the public internet, however, they cannot rapidly decrypt secure communications, not being equipped with quantum computers (unlike their military nanite brethren, which were not deployed on this mission).
Using this information, the Snakebot has been tasked to destroy all human infrastructure significantly more advanced than a shack or a tent, and to defend itself against counter-attack. Its target priority is to attack targets in the most militarily-capable areas first.
It is not interested in exterminating humanity. Individual humans are of little interest to it unless they are counter-attacking with any effectiveness, at which point the snakebot will simply eliminate the threat in the most expeditious manner possible given its options. However, neither will it attempt to preserve the life of humans or any other species.
If damaged, the snakebot's controlling nanites will use whatever materials available within the machine's structure and in the environment to effect repairs. The snakebot took around ten years to build beneath the Antarctic ice-cap, and the time to repair damage can be expected to be roughly inversely proportional to the amount of damage - the more damage, the more nanites will be required to repair it, and conversely the slower the repairs will be. Relatively minor damage can be expected to take as little as a few hours, and major damage such as the total loss of one reactor can be expected to take many months to a year or more.
When the snakebot has destroyed all modern human infrastructure (i.e. anything more advanced than a shack or a tent), or it is incapacitated to the point where it cannot continue its mission at all without first effecting repairs, the snakebot and all the engineering nanites on earth, including those controlling birds, will self-destruct. Don't worry, the birds won't be significantly harmed by their controlling nanites, either while being controlled or when the nanites controlling them self-destruct.
Any nanites captured by humans will self-destruct, of course.
Given the entire military and civilian resources of the modern world (like we wouldn't unite to get rid of this thing) , how can the Snakebot of Doom be defeated, or are we destined to be reduced to living in crude lean-tos and tents until we can rebuild our civilisation?