Alien virus I ignored spread worldwide (9)
I believe the answer is:
universal
'worldwide' is the definition.
(I know that worldwide can be written as universal)
'alien virus i ignored spread' is the wordplay.
'ignored' indicates named letters should be taken away.
'spread' indicates an anagram.
'alien'+'virus'='alienvirus'
'alienvirus' with 'i' removed is 'alenvirus'.
'alenvirus' anagrammed gives 'UNIVERSAL'.
(Other definitions for universal that I've seen before include "Widespread, worldwide" , "Found everywhere" , "affecting everyone" , "blanket" , "Worldwide or cosmic" .)