Digital protection is purely cosmetic (4,7)
I believe the answer is:
nail varnish
'cosmetic' is the definition.
(nail varnish is a kind of cosmetic)
'digital protection is purely' is the wordplay.
'digital protection' becomes 'nail' (a nail protects a digit).
'is purely' becomes 'varnish' (I can't explain this - if you can you should give a lot more credence to this answer).
'nail'+'varnish'='NAIL-VARNISH'
Can you help me to learn more?
(Other definitions for nail varnish that I've seen before include "Manicurist's cosmetic lacquer" , "Shiny fluid applied to the tips of one's digits" , "Lacquer applied to the body's extremities" , "Lacquer at one's fingertips" , "Substance applied to finger ends" .)