Worldwide spending on Internet advertising fell 5% in the most recent quarter, the second consecutive period in which the once-booming online ad market has shrunk, market-research group IDC said Wednesday.

IDC expects to see declines in the third and fourth quarters and predicts that spending on Internet search, display and classified ads may not significantly rebound until mid 2010.

"The good news: It seems like things are not going to get any worse anymore in the Internet ad industry," said IDC analyst Karsten Weide in a statement.

For the second quarter, IDC said worldwide ad spending was down 5% to $13.9 billion from $14.7 billion in the same period a year ago. The results are included in IDC's forthcoming Worldwide and U.S. Internet Ad Spend Report 2Q09.

The downturn hit most areas of the world, with the exception of the Asia Pacific region, including Japan, which saw slight gains in the most recent quarter.

U.S. Internet ad spending also declined for the second time in a row, down about 7% to $6.2 billion from $6.6 billion a year earlier. The pain was felt across all major formats, with search ads being least affected, display ads losing 12%, and classifieds shrinking 17%, the research group said.

IDC said ad sales for all major publishers declined, mostly at a double-digit rate, with search market leader Google Inc. (GOOG) the only exception. It posted low single-digit growth.

Worst affected were Monster Worldwide Inc. (MWW) owing to its exposure to the heavily hit classifieds business, and Time Warner Inc.'s (TWX) AOL unit, which suffered from weakness in display ads as well as internal sales problems.

In recent trading Wednesday, shares in Google were down 1% at $449.39, Monster was off 4.5% to $13.21, and Time Warner was down 2.7% at $27.32.

-By Scott Morrison, Dow Jones Newswires; 415-765-6118; scott.morrison@dowjones.com