They had a Chinese back door in the firmware. Don’t know if that’s still the case. techworm.net/…/lenovo-pcs-and-laptops-seem-to-hav… They’ve had several major (intentional) security flaws over the years. The rest of their Windows included software is cancer.
Lenovo PCs and Laptops seem to have a BIOS level backdoor
Lenovo PCs and Laptops seems to have hidden a rootkit in their BIOS
In the case of the soldiers in Iraq, China had installed an independent chip specifically for keylogging. I don’t know if replacing the boot loader would even solve that.