operation fast and furious, started during the bush years, was started to shut down the alleged iron pipeline of guns to mexican cartels. sometime in the last 2 years, that operation became operation gunrunner, where ATF offices encouraged gun dealers to conclude suspicious sales in the hopes of 'tracking them to major cartels', all in the official pretense of bringing down drug cartels. border patrol agent brian terry became a victim of this operation by being killed in a skirmish where some of these illicitly sold guns turned up.
Now, it turns out that not only did gunrunner appear to violate numerous laws, but an operation out of florida called 'castaway' also seems to have indications that ATF offices cleared weapons sales to known straw purchasers for export to central america.
Theres more detailed info here, http://www.justplainpolitics.com/showthread.php?31049-the-ATF-has-some-splaining-to-do
Good condensed version.