Our existance is like a CPU. It needs two things, a place to store the data and a system to access the data.
These aliens invaded the CPU through force update. To give it permission to enter the body and get administrative authorities.
Through force update the CPU needs to be rebooted causing it to lost the previous data, the lost data is a bunch of puzzle pieces that can be put together into datas.
Though some data tends to be unreadable. That's when it needs a decoder and leads/codes to decode the data.
Disclaimer: this is totally innacurate.