Bug makes six hurry, in need of hospital (5)
I believe the answer is:
virus
'bug' is the definition.
(I've seen this before)
'six hurry in need of hospital' is the wordplay.
'six' becomes 'VI' (Roman numerals).
'hurry' becomes 'rush' (synonyms).
'in need of' indicates named letters should be taken away.
'hospital' becomes 'H' (abbreviation for hospital on maps).
'rush' with 'h' taken away is 'rus'.
'vi'+'rus'='VIRUS'
'makes' acts as a link.
(Other definitions for virus that I've seen before include "Harmful agent to animals and computers" , "Ultramicroscopic infectious agent" , "One infecting human, computer" , "Corrupting influence" , "Microscopic infectant" .)