Internet ad spending in the United States decreased for the third consecutive quarter this year, down 4 percent to US$6.4 billion year-over-year, according to new data from IDC.

Worldwide online ad dollars slightly dropped 1 percent to $14.7 billion over the period.

Although still in decline, those figures showed an improvement compared to the prior quarter's drops of 7 percent and 5.6 percent, in the United States and worldwide, respectively. IDC said online advertising may have begun to bounce back, and it expected the U.S. market to slip again in the fourth quarter, only by about 1 percent, before actual growth is expected to return in the first and second quarters of 2010, MediaPost reported.

Other researchers also predict a rebound in 2010 for online advertising. eMarketer revised its online ad forecast for 2009 downward and expects a moderate growth in the next two years, with spending up 5.6 percent and 6.6 percent, respectively, according to MediaPost.