A spokeswoman for parent company AOL Time Warner (AOLTW) declined to comment on whether Colburn quit or was fired.
News of Colburn's departure comes as the deadline for executives to sign off on their latest quarterly earnings with the US Securities and Exchange Commission (SEC) rapidly approaches.
Although executives at AOLTW have said that they intend to press for the validity of the company's latest earnings report by the SEC's deadline today (14 August), this morning they still had not done so. However, the spokeswoman said that the company would be announcing its filing status by this afternoon.
AOLTW already faces a significant loss in investor confidence as both the SEC and the US Department of Justice have recently launched investigations into the company's accounting practices. The probes were spurred by a series of articles in the Washington Post last month alleging that the company engaged in a string of unusual deals in an effort to shore up revenues in its ailing AOL Internet unit.
Colburn's departure heightens speculation over allegedly dodgy deals that were forged under his rein.
The Post reported in its online edition today that Colburn was relieved of his day-to-day duties in business affairs late last month and moved to strategy issues instead. His exit came just days after AOL appointed a new chief executive, Jonathan Miller.