The keylogger was found by a security researcher, Michael Myng, inspecting Synaptics software looking for a way to control keyboard backlights.
THE KEYLOGGING FEATURE IS PART OF TOUCHPAD DRIVERS OF ABOUT 460 HP NOTEBOOK AND LAPTOPS models released from 2012. It is worth to mention that the keylogger IS NOT ACTIVE and in fact it is a debugging feature for software and hardware development purposes.
Needless to say keeping this feature built into a public released drivers, even if it is disabled by default, it is still A BIG RISK FOR SECURITY since an attacker, that already has admin rights of the machine, might be able to enable and make use of the feature.
Mr. Myng reached HP regarding the issue and they acknowledged it releasing very quickly a security bullettin and updated drivers.