By Andrew Brandt
PC gamers have a new threat to contend with, one that has your personal information in its crosshairs and you can’t dispatch with a sniper rifle or BFG9000: A Trojan designed to steal game passwords that uses Microsoft’s own graphics engine, DirectX, against you.
The Trojan, which appears to have originated in China, modifies one or more of the DirectX driver files — such as DirectSound, Direct3D, or DirectDraw — so it only loads when Windows fires up the modified DirectX driver. Because DirectX is typically used by games, it means this sleeper cell Trojan activates when you fire up a PC game, then terminates when you stop playing. As a result of using this unusual load point to start itself up, instead of a more typical Run key or Services entry in the Windows Registry, the Trojan is unusually low key.
In our tests, the installer drops one or more randomly named DLLs (the keylogger component) in the c:\windows\system directory, then modifies one or more DirectX files. Each modified DirectX file is used to load one keylogger payload, so if the installer happens to drop four keyloggers, it will also modify four DirectX files. It also adds instructions that call functions from another, unmodified, legitimate system file named mscat32.dll. MSCAT32 is completely benign: Windows uses mscat32.dll to create Microsoft Cabinet .cab files, which are similar to .zip archive files. We’ve named this aide-du-vol Trojan-PWS-Cashcab (though some of our competitors call it Kykymber).
As a result of the modifications, the keylogger component loads whenever any program initializes the modified DirectX driver file. Fortunately, it also loads when you run the DirectX Diagnostics program included with DirectX, DxDiag (click Start, Run, then type dxdiag and click OK to start it up). That’s also the easiest way to determine if your PC is infected.