The issue with that is that it doesn't match up well with the actual DNA work they've done on the virus - checking it out for signs of human 'adjustments'. They haven't found those tell-tales. Like, at all.
EDIT: I'm talking specifically about genetic alteration. I suppose 'studied in a lab, unmodified, and accidentally released' is a possibility, but WHO doesn't seem to think that's likely either.
And the virus is VERY close to one they've found in bats. The current theory is that the difference comes because it jumped from bats to...something?...then to people.
....also what Beadle said. ^_^