Revised figures in the latest UNAIDS study slashed an estimate for total infections this time last year to 32.7 million from 39.5 million cases, the number given in the agency's 2006 report.
"The single biggest reason for the reduction in global HIV prevalence figures in the past year was the recent revision in India after an intensive reassessment of the epidemic in that country," UNAIDS said in its report.
The number of people worldwide infected with HIV in 2007 totalled 2.5 million people and 33.2 million are now living with the virus, the report said. More than two million people died from the disease in 2007.
"Reliable public health data are the essential foundation for an effective response," said Kevin De Cock, head of HIV/AIDS at the World Health Organisation.
"We need to continue investing more in all countries and all aspects of strategic information relating to health," he added.
Numbers of people living with the virus were levelling out and the percentage of the population affected was now in decline, the report said.
Two-thirds of new infections were recorded in sub-Saharan Africa, although the overall number now infected in the region -- where three-quarters of the world's AIDS deaths have occurred -- was down by 1.7 million this year.
About 22.5 million people living in Africa have HIV/AIDS, 68 percent of the global total, the report said.
In Asia there are now 4.9 million cases, up 440,000 from last year. Indonesia has the fastest growing epidemic on the continent, while the number of HIV cases in Vietnam has more than doubled between 2000 and 2005.
The Caribbean is the second worst-hit region of the world in per capita terms with one percent of adults -- 230,000 people -- carrying the virus, according to the report.
The year 2007 has seen 11,000 deaths and 17,000 new infections in the island region so far, it said.