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CIAC Advisory number A- 33
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The Computer Incident Advisory Capability
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Informational Bulletin
Virus Propagation in Novelle and Other Networks
September 21, 1990, 1000 PST Number A-33
Problem: Virus propagation on write-protected file systems
Types: Many known viruses, most frequently variants of the Jerusalem
(Israeli) virus
Platform: MS-DOS computers
Damage: Files that use software write-protection schemes cannot be
assumed safe from damage due to virus infection
Symptoms: Virus infection on write-protected files
Detection: VIRHUNT, RESSCAN, CodeSafe, Vi-Spy, IBM Scan, FPROT
Eradication: VIRHUNT, CodeSafe, FPROT, and others (see text in p. 2 of
this bulletin for recommended procedures)
Critical Virus Propagation Facts
This bulletin is to warn of a virus threat to networks for MS-DOS
systems. File servers (e.g., Novell file servers) use attribute bits
to perform write protection on files stored on server machines. Many
viruses will clear these attribute protection bits before they attempt
infection, thus circumventing the write protection scheme. Thus,
write-protecting a program does not guarantee that the file is not
infected with the virus.
The following is a common scenario reported to CIAC: a floppy infected
with the Jerusalem-B virus is inserted into a user's PC attached to a
Novell network. Once this virus is executed, it resides in the PC's
memory. When the user attempts to logon to the file server (running
the program login.exe), the virus infects this program, even though the
program is write-protected. Login.exe is a shared program that is
executed by each user as s/he connects to the Novell network. Thus,
each time a user logs in to the network, his/her machine immediately
becomes infected with the Jerusalem-B virus. The network allows the
Jerusalem-B virus to spread considerably more quickly than if it had
spread through exchange of floppy disks.
When someone disinfects a system of PCs or PC clones on a Novell or
similar file system, CIAC recommends the following procedures:
1) Detect the virus using one of the recommended packages for
detecting and identifying the virus. Determine exactly which virus has
infected the system, and that all virus types have been detected.
Contact CIAC if you need assistance.
2) Deactivate the network connecting the PCs/PC clones together.
This includes shutting down the file servers and unmounting the
partitions from the users' PCs/PC clones.
3) Disinfect the server machines using an anti-virus package known
to be effective against the detected virus. Alternately, reformat the
server disks and re-install the system from original diskettes, then
restore the data files from a recent backup. Do not attempt to restore
programs (i.e., executable files) from a backup, as this is likely to
reinfect your system.
4) Disinfect each user's PC/PC clone using the same procedure as
in step 2.
5) Verify that the virus does not reside on the file server or any
user's PC/PC clone.
6) Bring the network file system back up.
For additional information or assistance, please contact CIAC:
Tom Longstaff
(415) 423-4416 or (FTS) 543-4416
FAX: (415) 423-0913 or (FTS) 543-0913
Send e-mail to:
[email protected]
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