Stock price plummeted. Sales plunged. Official website was hacked. Amid escalating pressure, the batch number of Mengniu's tainted milk was finally exposed.

A screen grab of Mengniu's official website on Wednesday night. The website was hacked into at 11pm for about an hour. [Photo/21cbh.com]

The batch number of the faulty milk caused by raw milk produced by cows eating mildewed feed is 20111018G8101DFA//VB-VF, Beijing Times reported Thursday, citing a letter dated Dec 26 sent from Mengniu to some of the supermarkets in Beijing.

The exposed number is different from those shown in pictures uploaded online by several consumers on Tuesday, but Wang Dingmian, chairman of the Guangzhou Dairy Association, says it's impossible that a vat of Mengniu's tainted raw milk produces only one batch of finished products considering the size of the vats.

The latest faulty products put China's biggest dairy manufacturer under mounting pressure.

Mengniu's stock price shrank by nearly a quarter Wednesday, the first trading day after the scandal broke, and its sales in Beijing plunged by almost 40 percent in the past two days. Hackers usurped control of its official website Wednesday night for more than an hour and left a note, calling Mengniu a "national disgrace".

The General Administration of Quality Supervision, Inspection and Quarantine published on Dec 24 the results of a random check on dairy products, which found the amount of aflatoxin in a 250-milliliter carton of milk produced by Mengniu on Oct 18 in Meishan, Sichuan province, was more than twice the national limit.