Hackers work digitally. Nonetheless, they are capable of physically damaging critical infrastructure through cyber attacks. This infrastructure is controlled by SCADA or ICS systems and connected to the internet through computer networks.
A malicious intruder could, for example, deliberately open locks and bridges, toggle railroad switches, or make the instruments in a (nuclear) power plant display incorrect readings. Although the risk of this actually happening in the Netherlands is quite low, the possibility alone is enough to test for and secure against it.