If you think you may be infected, Kaspersky Labs has released a free tool for Windows users (all versions, 32 and 64-bit) called TDSSKiller which will detect and remove TDL4 rootkits / bootkits. It can be downloaded here.
TDSSKiller also detects other TDSS-family rootkits such as TDL2 / TDL3, and unknown rootkits by analyzing for:
- Hidden or Blocked services
- Hidden or Blocked files
- Forged files
- Rootkit.Win32.Backboot.gen (generic / unknown MBR infection)
If you have no luck with TDSSKiller, you may wish to try Norman TDSS Cleaner, Avast's aswMBR Tool, or HitMan Pro, which also claim to detect and remove TDL3, TDL4 and its variants.