Can a 32-bit antivirus program protect you from 64-bit threats

It all depends on how the antivirus software works.

32-bit programs might not be able to interoperate directly with running 64-bit processes (other than through the Windows API), but they do still have access to the entire file system including files containing 64-bit code. So technically yes a purely 32-bit antivirus could still do it's job and identify viruses in 64-bit files via traditional file-scanning techniques.

However...

The fact that an application is installed into C:\Program Files (x86) doesn't actually mean it's 32-bit.

• You can have 64-bit applications running from C:\Program Files (x86)

• You can have 32-bit applications running from C:\Program Files.

• Many applications actually contain a mix of 32-bit and 64-bit files but install to only either C:\Program Files (x86) or C:\Program Files. A good example is VMware Workstation. On my 64-bit system, it installs to C:\Program Files (x86)\VMware\VMware Workstation. The files installed to that location are a mix of 32-bit and 64-bit EXE/DLL files, among other random files.

So what's the name and version of the antivirus software you're running? Chances are good that it does have 64-bit components in there and that they are being used on your 64-bit system.

You can easily check what bitness your background antivirus processes are running as by launching Resource Monitor. You just need to make sure the Platform column is showing (right click on any column then click on Select Columns...:

Look for your antivirus processes in the list see what bitness they're running as. You might find that the antivirus GUI runs as a 32-bit process, yet the engine itself runs as a 64-bit process. That's pretty common.

Let us know what you discover ;-)