The number of U.S. jobs posted online dropped by 507,000 in December to 3.9 million, according to The Conference Board's measure of online help-wanted ads released today. This is the first time since the summer of 2006 that the measure has fallen below 4 million.

"The sharp December drop in online advertised vacancies is another indication that the economy has not reached bottom," said Gad Levanon, senior economist at The Conference Board. "The widespread nature of the decline in employers' demand for workers — both across geographies and across occupations — does not bode well for an employment upturn in the first half of 2009."