Advertising giant WPP was performing well on Thursday, helped by an upgrade from UBS from neutral to buy.The broker also hiked its target price from 675p to 840p, suggesting a significant upside to the current price of 716.5p (at yesterday's close)."We believe WPP offers favourable risk-reward," said analysts at the Swiss bank. "In our opinion, a near-term slowdown in Europe is already in consensus expectations, medium-term growth is secured through global exposure, and valuation and cash returns are supportive, leaving the stock with greater potential upside in a stronger market than professional publishers, but with less risk than broadcasters."WPP's organic growth in the 12 months to the end of 2012 will be driven by around 2% global economic growth, as opposed to the 1% global recession in 2009 which drove an 8% organic decline, notes the broker.With the stock trading at 9.5 times 2012 earnings, and peers trading at a multiple of 11.5, UBS argues that WPP is "cheap even on our conservative forecasts".BC