The landgrab for internet advertising companies is set to continue, with Microsoft and Sir Martin Sorrell's WPP each said to be weighing a $1 billion (£500m) bid for 24/7 Real Media.

Shares in the Nasdaq-listed group, which specialises in tracking and maximising the success of online ad campaigns, surged 35 per cent in pre-market trading in New York, to $13.39, valuing the company at about $685 million.

A deal would follow Google’s $3.1 billion acquisition of DoubleClick, the largest broker of online display – or banner – advertising last month and Yahoo’s agreed purchase of RightMedia, a rival broker that specialises in placing adverts on smaller websites, for $680 million (£340m), which was announced over the weekend.

Both WPP and Microsoft sought to buy DoubleClick and voiced concerns over competition issues after Google’s agreed acquisition.

Microsoft, which has fallen off the pace set by Google in online search and advertising, is also understood to have matched Google’s $3.1 billion offer for the company, only to be rebuffed by DoubleClick.

London-listed WPP, meanwhile, is one of Google's largest customers, having spent an estimated $200 million on Google's search advertising in 2006, a 33 per cent increase on the previous year.

Google’s acquisition of DoubleClick, which buys and sells advertising, effectively means that the internet company has become a competitor to WPP, the world’s second-largest advertising services group.

Other potential online advertising targets include aQuantive and ValueClick.

Microsoft and WPP did not immediately respond to requests for comment.

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