Yahoo!’s CFO warned of a weakening in online advertising demand yesterday, causing jitters among investors in major US internet stocks.

According to Reuters, Sue Decker told a Goldman Sachs conference in New York that “a little bit of weakness” in automotive and financial advertising had emerged in the last few weeks, but it was unclear if it was just a temporary phase or part of a wider trend.

We’re seeing it enough to say something,” she said. “I don’t want to overplay it either.

Decker said the company expected to report Q3 earnings in the lower half of the range that the company predicted in July. Shares in the portal dropped by around 10% on the news, while stocks in Google, eBay and Amazon were also affected.

Analysts related the warning to a slowdown in the housing market, as well as troubles in the US car industry, but were unclear whether the weakness was specific to Yahoo! or industry-wide.

We’ll be watching results from Google and other internet companies to see if this is indeed just a blip, or just a specific issue,” Richard Williams, director of equity research at interdealer broker ICAP in New York, told the news agency.