Nintendo of America has issued a statement with respect to the strange 'Red Tulip' emails that have been circulating throughout Animal Crossing: Wild World for Nintendo DS via the Nintendo Wi-Fi Connection.

According to reports, the items appearing attached to a blank letter upon disconnecting from the WFC become irremovable objects if placed inside the player's home area. This made Nintendo to come up with an official statement explaining the glitch.
It says;
We have isolated the problem and determined that there was a temporary error with the upload tool when this letter was posted. Thankfully, we have been able to limit the number of people affected by removing the related file from circulation. Players who have received the letter should delete it before placing the Red Tulip anywhere in their characters' homes.
Phew! So it wasn't a user scripted virus after all. But what then about those who are already been affected? Nintendo promised that it would look in to the matter and investigate it.
Ok, got your point.