Shares in Yahoo, the internet portal, were marked down more than 5 per cent on Friday morning after it emerged that AT&T was trying to renegotiate a five-year-old agreement under which the US telecoms giant has sold its broadband DSL service under the joint AT&T Yahoo brand name.The negotiations between the two companies reflect the realities of a shifting power balance, not only between the two companies, but also between telecommunications groups and the internet portals that dominated early attempts to commercialise the worldwide web.
