Dodgy installer drops Trojan in Japanese Buffalo update

Buffalo in Japan is red-faced after its Website shipped Trojan-infected Windows driver updates for a bunch of its peripherals, including broadband routers, home NAS, and Bluetooth mice.
According to this notice (Google translation here), the installers were modified to include Infostealer.Bankeiya.B, which steals bank account data.
Symantec reports that Buffalo moved quickly, removing the compromised files on the same day, May 27, as they appeared.
As a result, the ten compromised files were only downloaded 856 times, from 540 unique IPs.
Symantec spotted two variants in the attack. In one, the compromised files had the self-extracting setup.exe RAR file modified to execute a malicious DLL during installation. This linked to a second DLL that downloaded and installed Infostealer.Bankeiya.B.
In the second, “a Buffalo installer is included within Infostealr.Bankeiya.B and Infostealer.Bankeiya.B is made to look like a legitimate installer. This means that running the installer will drop the setup.exe file for the legitimate driver as well as a component of the Trojan that drops a malicious .dll which downloads the main component of Infostealer.Bankeiya.B.”
Users that downloaded the update have been told not to use Internet banking until they've disinfected their machines. McAfee and Symantec products catch the Trojan, Buffalo says.