From CBS News' Maria Gavrilovic:
(CHICAGO) - Shortly after 3am, Barack Obama supporters received a text message announcing that the soon-to-be Democratic nominee had chosen Joe Biden as his running mate.
As promised, supporters were the first to receive official confirmation of Obama's decision, however, late Friday evening, most major media outlets were reporting that it was Biden.
Obama and Biden will appear together with their spouses in Springfield this afternoon. Although Biden endorsed Obama months ago, this will be the first time that the two senators will appear together since Obama secured the nomination.
It didn't take the McCain campaign long to react Obama's decision - just a few hours after the Biden text message was sent, the McCain camp rolled out an ad highlighting his criticism of Obama during the primary.
The ad features a clip from a debate, where ABC's George Stephanopoulos asks Biden to clarify a statement that he had made about Obama's experience.
"You were asked is he ready. You said 'I think he can be ready, but right now I don't believe he is. The presidency is not something that lends itself to on-the-job training,'" Stephanopoulos asked.
"I think that I stand by the statement," Biden replied.
The McCain campaign signaled that they will continue to use Biden's comments during the primary against Obama.
"There has been no harsher critic of Barack Obama's lack of experience than Joe Biden… Biden has denounced Barack Obama's poor foreign policy judgment," McCain spokesman Ben Porritt said this morning.
Hillary Clinton released a statement as well, praising Obama's choice and highlighting Biden's experience.
"Senator Obama has continued in the best traditions for the Vice Presidency by selecting an exceptionally strong, experienced leader and devoted public servant."