Ruffian provides company online (5)
I believe the answer is:
yahoo
I believe this clue is a double definition.
'ruffian' is the first definition.
(thesaurus)
'company online' is the second definition.
(Yahoo! is an internet company)
'provides' acts as a link.
(Other definitions for yahoo that I've seen before include "[WHOOPEE] !" , "Boorish louts" , "Lout, boorish person" , "Human-looking beast in Gulliver's Travels: search engine conglomerate" , "A Swiftian lout" .)