Criminal gangs using hijacked computers are behind a surge in unwanted emails peddling sex, drugs and stock tips. The number of "spam" messages has tripled since June and now <A HREF="http://www.cnn.com/2006/WORLD/europe/11/27/uk.spam.reut/index.html">accounts for as many as nine out of ten emails</A> sent worldwide, according to U.S. email security company Postini. As Christmas approaches, the daily trawl through in-boxes clogged with offers of fake Viagra, loans and sex aids is tipped to take even longer.