Up-to-date virusscanner from McAfee for free: 

Scanpm.exe runs on dos. I use it on win98 systems. 

Outside of windows it needs himem.sys. ( And load smartdrv first to make
it faster. ) You can also use it inside of windows.

Installing: 

Download scanpm.zip, pkunzip.exe and install.bat from here.
Save them to the desktop. 
Run install.bat.
A new folder 'scanpm' is created on the desktop.
You can delete scanpm.zip, pkunzip.exe and install.bat.

Updating:

Then running 'update.bat' within that directory does an automatic update.
This must be done from within windows, it uses the built-in ftp program.  
( 'download.txt' is input for the ftp-command in 'update.bat' ) And of 
course it needs an open internetconnection.

Getting the dat-files takes about 15 minutes on a 56k-bit modem 
connection.

Using:

( You must update at least once before using it. )

Running scan.bat will scan the c: drive.
You can also drag individual files or folders to scan.bat.

--- /Jasper, may 2004

============================================================
Note:

With the release of the 4367
   DATs, on Wednesday June 16, 2004, customers began to notify AVERT and
   Network Associates Support of machines failing to initialize after
   installing or updating to the 4367/4.1.60 configuration. The two
   components are not compatible and the 4.1.60 engine needs to be
   removed and an update needs to take place to the 4.3.20 engine.
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scanpm.zip has the new version of scanpm.exe now.
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2007-06: look at Engine.txt