Reston, Va.--Proxicom Inc. has given formal notice to Compaq Computer Corp. that it has received a superior buyout offer from Dimension Data Holdings plc, jeopardizing Compaq's recently announced purchase of Proxicom. Houston-based Compaq has three business days to make a counteroffer. Epsom Downs, South Africa-based Dimension Data has made a $448 million equity offer for Proxicom, topping Compaq's original $226 million equity bid. Dimension Data in recent months has said that it intends to strengthen its U.S. IT consulting presence, and its management views acquiring Proxicom as an expedient way to do so.