MBR is basically the Master Boot Record. It's the first 512 bytes on an MBR partitioned disk. All you have to do is write 512 bytes to the first block and you've overwritten the MBR. It's trivial to not only do this but also do undo this.
More than likely the individual/group does more than just overwriting the MBR, so a reinstallation of Windows is necessary to undo the damage done (which is often the case after bad infections anyway), but the author didn't mention that, they seemed to imply you must reinstall all of Windows in order to write a 512 bytes to the start of a disk.
I mourn the death of technology journalism written by journalists who actually understand the technology they're covering.