Wow is not and never will be free.
If you got a supposedly free (non monthly payment) version im assuming you got one that connects to a private server.
If thats the case then no suprise it was a virus.
Buy it out a shop or online at blizzards website then sign up for the monthly payments after the initial 30days free.
^ What he said.
From what I read, your saying you want it to be played as a browser game.
Simple answer. No. Impossible. Too big. Not to be mean, but WoW isn't RuneScape. (Which i'd rather play besides WoW )
WoW will never be free, from what it looks like plasmastorm is right you may have downloaded a private server which gave you the virus. I highly doubt that the real WoW client would have gave you a virus.