Obama leads online race to White House

BarackObama.com garnered 2.3 million unique visitors during the month, compared to McCain's 563,000, Nielsen reported on Monday.

"Barack Obama got a head start during primary season in using the Web effectively to garner support, both in terms of votes and donations," said Jon Gibs, vice president, media analytics, Nielsen Online.

Obama's campaign placed considerably more image-based online advertising impressions in May, with McCain's campaign leading in search sponsored links. The democratic nominee garnered 105 million image-based impressions, while McCain raked 8,551 million.

McCain did receive nearly 5 times more sponsored link impressions at 5,447 million impressions versus Obama's 1,806 million.

"It will be interesting to see how things shape up online as we head toward the general election. McCain's Web site includes both video and social networking capabilities, which have proven successful for his Democratic rival," Gibs said.

"Now that the contest has shifted away from the primary season, McCain may gain more traction online. But it remains to be seen if his core demographic will embrace the medium the way Obama's has."