An article carried by Wired originating from Reuters says that the Chinese now believe that the SARS virus crossed over to humans from civet cats.

The cats are considered a delicacy in certain parts of China (yes, that's delicacy, as in food, not pets). They are believed to be a carrier, and thus do not show symptoms of the disease, but it does appear to be present in fecal matter and respiratory secretions, which is how people are believed to have come into contact with them.