diff --git a/omaha/hammer-brave.bat b/omaha/hammer-brave.bat
deleted file mode 100644
index e6ea678a..00000000
--- a/omaha/hammer-brave.bat
+++ /dev/null
@@ -1,122 +0,0 @@
-@echo off
-
-:: Hammer does not need this variable but the unit
-:: tests do.
-set OMAHA_PSEXEC_DIR=%ProgramFiles(x86)%\pstools
-
-:: Set VS environment variables.
-call "%VS140COMNTOOLS%..\..\VC\vcvarsall.bat" x86 10.0.10586.0
-
-setlocal
-
-rem -- Set all environment variables used by Hammer and Omaha. --
-
-:: VS2003/VC71 is 1310 (not supported by the current build).
-:: VS2005/VC80 is 1400 (not supported by the current build).
-:: VS2008/VC90 is 1500 (not supported by the current build).
-:: VS2010/VC10 is 1600 (not supported by the current build).
-:: VS2012/VC11 is 1700 (not supported by the current build).
-:: VS2013/VC12 is 1800.
-:: VS2015/VC14 is 1900.
-
-if "%VisualStudioVersion%"=="" goto error_no_vc
-if "%VisualStudioVersion%"=="12.0" goto vc120
-if "%VisualStudioVersion%"=="14.0" goto vc140
-goto error_vc_not_supported
-
-:vc120
-set OMAHA_MSC_VER=1800
-goto set_env_variables
-
-:vc140
-set OMAHA_MSC_VER=1900
-goto set_env_variables
-
-:set_env_variables
-
-:: Set signtool arguments
-set SIGNTOOL_ARGS="sign /t http://timestamp.digicert.com /fd sha256 /sm"
-
-:: Change these variables to match the local build environment.
-
-:: Directory where the Go programming language toolchain is installed.
-set GOROOT=C:\Go
-
-:: Directory where AtlServer files are.
-set OMAHA_ATL_SERVER_DIR=c:\atl\
-
-:: This will depend on your OS. If this version of the .Net framework came with
-:: the OS, then set it to the framework directory
-:: (something like C:\Windows\Microsoft.NET\Framework\v2.0.50727).
-:: Otherwise, set it to the directory where the .NET framework is installed.
-set OMAHA_NET_DIR=%WINDIR%\Microsoft.NET\Framework\v2.0.50727
-
-:: This directory is needed to find mage.exe tool, which is the .Net manifest
-:: generating tool. This tool ships as part of the Windows SDK.
-:: However, newer versions of mage.exe can't targer older versions of .Net
-:: framework. If there is a need for the click-once application to run on older
-:: versions of the .Net framework, then an older version of the Windows SDK
-:: needs to be installed and this environment variable point to that directory.
-set OMAHA_NETFX_TOOLS_DIR=%WindowsSDK_ExecutablePath_x86%
-
-:: This directory is needed to find protoc.exe, which is the protocol buffer
-:: compiler. From the release page https://github.com/protocolbuffers/protobuf/releases,
-:: download the zip file protoc-$VERSION-win32.zip. It contains the protoc
-:: binary. Unzip the contents under C:\protobuf.
-set OMAHA_PROTOBUF_BIN_DIR=C:\protobuf\bin
-
-:: This directory is needed to find the protocol buffer source files. From the
-:: release page https://github.com/protocolbuffers/protobuf/releases, download the zip
-:: file protobuf-cpp-$VERSION.zip. Unzip the "src" sub-directory contents to
-:: C:\protobuf\src.
-set OMAHA_PROTOBUF_SRC_DIR=C:\protobuf\src
-
-:: Directory where Python (python.exe) is installed.
-set OMAHA_PYTHON_DIR=C:\Python24
-
-:: Directory in WiX where candle.exe and light.exe are installed.
-set OMAHA_WIX_DIR=%ProgramFiles(x86)%\WiX Toolset v3.11\bin
-
-:: Root directory of the WTL installation.
-set OMAHA_WTL_DIR=C:\wtl\
-
-set OMAHA_PLATFORM_SDK_DIR=%WindowsSdkDir%\
-set OMAHA_WINDOWS_SDK_10_0_VERSION=%WindowsSDKVersion:~0,-1%
-
-:: Directory which includes the sign.exe tool for Authenticode signing.
-set OMAHA_SIGNTOOL_SDK_DIR=%WindowsSdkDir%\bin\10.0.15063.0\x86
-set PYTHONPATH=%OMAHA_PYTHON_DIR%
-
-:: Directory of Scons (http://www.scons.org/).
-set SCONS_DIR=C:\Python24\Lib\site-packages\scons-1.3.1
-
-:: Directory of the Google's Software Construction Toolkit.
-set SCT_DIR=C:\swtoolkit
-
-set PROXY_CLSID_TARGET=%~dp0proxy_clsids.txt
-set CUSTOMIZATION_UT_TARGET=%~dp0common\omaha_customization_proxy_clsid.h
-
-
-set OMAHA_PSEXEC_DIR=C:\pstools
-
-rem Force Hammer to use Python 2.4.  (The default of Python 2.6 exposes some
-rem bugs in Scons 1.2, which we currently use.)
-set PYTHON_TO_USE=python_24
-call "%SCT_DIR%\hammer.bat" %*
-
-if /i {%1} == {-c} (
-  del /q /f "%PROXY_CLSID_TARGET%" 2> NUL
-  del /q /f "%CUSTOMIZATION_UT_TARGET%" 2> NUL
-)
-
-goto end
-
-:error_no_vc
-echo VisualStudioVersion variable is not set. Have you run vcvarsall.bat before running this script?
-goto end
-
-:error_vc_not_supported
-echo Visual Studio version %VisualStudioVersion% is not supported.
-goto end
-
-:end
diff --git a/omaha/hammer.bat b/omaha/hammer.bat
index 593a10de..bde32b0b 100644
--- a/omaha/hammer.bat
+++ b/omaha/hammer.bat
@@ -1,12 +1,5 @@
 @echo off
 
-:: Hammer does not need this variable but the unit
-:: tests do.
-set OMAHA_PSEXEC_DIR=%ProgramFiles(x86)%\pstools
-
-:: Set VS environment variables.
-call "%ProgramFiles(x86)%\Microsoft Visual Studio\2017\Community\VC\Auxiliary\Build\vcvarsall.bat" amd64_x86 10.0.18362.0
-
 setlocal
 
 rem -- Set all environment variables used by Hammer and Omaha. --
@@ -46,53 +39,91 @@ goto set_env_variables
 
 :set_env_variables
 
-:: Set signtool arguments
-set SIGNTOOL_ARGS="sign /t http://timestamp.digicert.com /fd sha256 /sm"
-
 :: Change these variables to match the local build environment.
 
+:: Hammer does not need this variable but the unit tests do.
+if not defined OMAHA_PSEXEC_DIR (
+  set "OMAHA_PSEXEC_DIR=%ProgramFiles(x86)%\pstools"
+)
+echo OMAHA_PSEXEC_DIR: %OMAHA_PSEXEC_DIR%
+
 :: Directory where the Go programming language toolchain is installed.
-set GOROOT=C:\go
+if not defined GOROOT (
+  set "GOROOT=C:\go"
+)
+echo GOROOT: %GOROOT%
 
 :: This directory is needed to find protoc.exe, which is the protocol buffer
-:: compiler. From the release page https://github.com/protocolbuffers/protobuf/releases,
+:: compiler. From the release page https://github.com/google/protobuf/releases,
 :: download the zip file protoc-$VERSION-win32.zip. It contains the protoc
 :: binary. Unzip the contents under C:\protobuf.
-set OMAHA_PROTOBUF_BIN_DIR=C:\protobuf-2020-sep-rebase\bin
+if not defined OMAHA_PROTOBUF_BIN_DIR (
+  set OMAHA_PROTOBUF_BIN_DIR=C:\protobuf\bin
+)
+echo OMAHA_PROTOBUF_BIN_DIR: %OMAHA_PROTOBUF_BIN_DIR%
 
 :: This directory is needed to find the protocol buffer source files. From the
-:: release page https://github.com/protocolbuffers/protobuf/releases, download the zip
+:: release page https://github.com/google/protobuf/releases, download the zip
 :: file protobuf-cpp-$VERSION.zip. Unzip the "src" sub-directory contents to
 :: C:\protobuf\src.
-set OMAHA_PROTOBUF_SRC_DIR=C:\protobuf-2020-sep-rebase\src
+if not defined OMAHA_PROTOBUF_SRC_DIR (
+  set OMAHA_PROTOBUF_SRC_DIR=C:\protobuf\src
+)
+echo OMAHA_PROTOBUF_SRC_DIR: %OMAHA_PROTOBUF_SRC_DIR%
 
 :: Directory where Python (python.exe) is installed.
-set OMAHA_PYTHON_DIR=C:\Python27
+if not defined OMAHA_PYTHON_DIR (
+  set OMAHA_PYTHON_DIR=C:\Python27
+)
+echo OMAHA_PYTHON_DIR: %OMAHA_PYTHON_DIR%
 
 :: Directory in WiX where candle.exe and light.exe are installed.
-set OMAHA_WIX_DIR=%WIX%\bin
+if not defined OMAHA_WIX_DIR (
+  set "OMAHA_WIX_DIR=%WIX%\bin"
+)
+echo OMAHA_WIX_DIR: %OMAHA_WIX_DIR%
 
 :: Root directory of the WTL installation.
-set OMAHA_WTL_DIR=C:\wtl
+if not defined OMAHA_WTL_DIR (
+  set OMAHA_WTL_DIR=C:\wtl\files
+)
+echo OMAHA_WTL_DIR: %OMAHA_WTL_DIR%
 
-set OMAHA_PLATFORM_SDK_DIR=%WindowsSdkDir%\
-set OMAHA_WINDOWS_SDK_10_0_VERSION=%WindowsSDKVersion:~0,-1%
+if not defined OMAHA_PLATFORM_SDK_DIR (
+  set "OMAHA_PLATFORM_SDK_DIR=%WindowsSdkDir%\"
+)
+echo OMAHA_PLATFORM_SDK_DIR: %OMAHA_PLATFORM_SDK_DIR%
+
+if not defined OMAHA_WINDOWS_SDK_10_0_VERSION (
+  set "OMAHA_WINDOWS_SDK_10_0_VERSION=%WindowsSDKVersion:~0,-1%"
+)
+echo OMAHA_WINDOWS_SDK_10_0_VERSION: %OMAHA_WINDOWS_SDK_10_0_VERSION%
 
 :: Directory which includes the sign.exe tool for Authenticode signing.
-set OMAHA_SIGNTOOL_SDK_DIR="%WindowsSdkVerBinPath%\x86"
-set PYTHONPATH=%OMAHA_PYTHON_DIR%
+if not defined OMAHA_SIGNTOOL_SDK_DIR (
+  set OMAHA_SIGNTOOL_SDK_DIR="%WindowsSdkVerBinPath%\x86"
+)
+echo OMAHA_SIGNTOOL_SDK_DIR: %OMAHA_SIGNTOOL_SDK_DIR%
 
 :: Directory of Scons (http://www.scons.org/).
-set SCONS_DIR=C:\Python27\Lib\site-packages\scons-1.3.1
+if not defined SCONS_DIR (
+  set "SCONS_DIR=%OMAHA_PYTHON_DIR%\scons-1.3.1"
+)
+echo SCONS_DIR: %SCONS_DIR%
 
 :: Directory of the Google's Software Construction Toolkit.
-set SCT_DIR=C:\swtoolkit
+if not defined SCT_DIR (
+  set SCT_DIR=C:\swtoolkit
+)
+echo SCT_DIR: %SCT_DIR%
 
-set PROXY_CLSID_TARGET=%~dp0proxy_clsids.txt
-set CUSTOMIZATION_UT_TARGET=%~dp0common\omaha_customization_proxy_clsid.h
+set "PROXY_CLSID_TARGET=%~dp0proxy_clsids.txt"
+set "CUSTOMIZATION_UT_TARGET=%~dp0common\omaha_customization_proxy_clsid.h"
 
 rem Force Hammer to use Python 2.7
 set PYTHON_TO_USE=python_27
+set "PYTHONPATH=%OMAHA_PYTHON_DIR%"
+
 call "%SCT_DIR%\hammer.bat" %*
 
 if /i {%1} == {-c} (