The enzyme which cuts down the viral dna with no harm to bacterial chromosme is

Bacteria and restriction enzymes

,use enzymes to cut (and thereby destroy) foreign DNA (such as viral DNA), which would restrict the growth of the virus; own DNA is protected in some way (often by addition of methyl group CH3) to the sequence recognized by enzyme (thus preventing enzyme from binding there)

A, if i am wrong correct me

All of them are man made