This is a story from September of 2004. We don't yet know all the details. The overall view is that CBS News was given some memos purporting to pertain to President Bush's National Guard service. After a few of days of analysis by bloggers, it became apparent that the memos as released by CBS were modern forgeries, not documents typed in 1973. The fake documents were an attempt to deceive (successful for a while) and are rightfully called a hoax. This hoax had as its ultimate target all of us - it appeared to be an attempt to influence the upcoming election. Before that deception could occur the hoaxer had to fool CBS News. Seems that was not difficult.
Some, but not all, details are reasonably well-known.
There are still important details that are not known.
If you would like to see the fake memos for yourself, here they are.
Suggestion: study them closely to see if you can see the signs that screamed HOAX to those with enough background to recognize them.For deep details of the typographical analysis, see Dr. Joseph Newcomer's excellent dissection of the typography of the memos. He demonstrates quite scientifically that the memos were forgeries. He actually outlines, then uses, the scientific method to do it.
The Washington Post studied the memos and found numerous reasons to conclude that the memos were fakes (thelink is now gone).
Report of the Independent Review Panel headed by Dick Thornburgh