More than four million PCs have been enrolled in a botnet security experts say is almost 'indestructible'pThis article is from the a href="http://news.bbc.co.uk" title="Link to BBC News"BBC News website/a. © British Broadcasting Corporation, The BBC is not responsible for the content of external internet sites./p pa href="http://feedads.g.doubleclick.net/~a/Ohi4lbNm73ySNKEEpja8N0sJ4gk/0/da"img src="http://feedads.g.doubleclick.net/~a/Ohi4lbNm73ySNKEEpja8N0sJ4gk/0/di" border="0" ismap="true"/img/abr/ a href="http://feedads.g.doubleclick.net/~a/Ohi4lbNm73ySNKEEpja8N0sJ4gk/1/da"img src="http://feedads.g.doubleclick.net/~a/Ohi4lbNm73ySNKEEpja8N0sJ4gk/1/di" border="0" ismap="true"/img/a/pimg src="http://feeds.feedburner.com/~r/BbcNewsTechnologyFullFeed/~4/C-A-V_IoY4o" height="1" width="1"/