supernetting/summarization

A company got machine address 192.168.0.0/16 from ISP and the n/w admin created 2 subnets,as
192.168.1.0/24 and 192.168.2.0/24 ,and assigned addresses from these ranges to all machines and devices , as the problem the client/company may face other packests (192.168.3.0/24,192.168.4.0/24 ... so on) may send to the company's network... which creates loop problems...
I want to make sumerization of ...rest of all these networks...
to prevent the loop may occur ...
'''May these possible ? having summarize address
192.168.3.0
,192.168.4.0
,,,192.168.5.0
,,,,192.168.6.0 ...
....192.168.254.0
how will be done?
Need your guidance - Please

most easy way this is done in companies is making a null route to 192.168.0.0 and have all your other subnets advertised as more specific. this way all traffic to non-existing subnets will be dropped.