Fears about a spreading cyclical slowdown in some areas of online advertising and e-commerce reverberated through Wall Street on Thursday after ValueClick, which runs the largest independent online advertising network, pre-announced weak earnings for the latest quarter and slashed its financial forecasts for the rest of the year.

The surprise followed evidence from Ebay late the day before that economic pressures were starting to affect consumers’ online buying behaviour, with internet sales of cars taking a hit and buyers turning to lower-priced goods in all categories.