I am looking forward to finding out what the hell happened... I guess it was corruption in someway, rather than strictly an accident?
The tests reveal equine DNA in there. Presumably from horse meat.
One question people are asking, is "how did it take so long to spot that". Well, the response, for fear of defending the authorities is (a) The media have not yet found out how long it has been going on, but more importantly (b) There is no test for is there something else in there. Before you do the test you have to have suspicion of what you are looking for? The tests are simply is x in there. Is y in there. Is z in there etc., etc.
So I am guessing there was a tip off somewhere which led the scientists to make the discovery. That, or the cows ate a load of horse meat? No actually that is silly, because the equine (horse) DNA would be completely digested in the gut and never arrive in the meat of the cow. ....Unless the cows ate the horses and were slaughtered stomachs filled and the cow's intestines were included in the beefburger "mix" . It is important to remember that when shops say "100% beef" they only ever meant "100% from a cow". That would include grizzle, blood vessels etc. etc. Not actual prime steak.
...but surely it is a little amusing to see distressed parents who have been feeding their kids bargain beefburgers when they learn that this DREADFULLY unhealthy meal has actually been contaminated with something... a little less unhealthy. Horse meat, per say, is a little less bad for you than beef meat.