Criminal gangs using hijacked computers are behind <A HREF="http://www.eweek.com/article2/0,1895,2064450,00.asp?kc=EWNAVEMNL112806EOAD">a surge in unwanted emails</A> peddling sex, drugs and stock tips in Britain. The number of "spam" messages has tripled since June and now accounts for as many as nine out of 10 emails sent worldwide, according to U.S. email security company Postini.