http://www.fudzilla.com/news/38466-lenovo-caught-reinstalling-bloatware
One more reason to build it yourself.
Basically, before booting Windows, the Lenovo Service Engine (LSE) built into the laptop's firmware replaces Microsoft's copy of autochk.exe with Lenovo's version. Lenovo's version then ensures that LenovoUpdate.exe and LenovoCheck.exe are present in Windows' system32 directory, with full administrative rights.
One more reason to build it yourself.