You need to describe the messages more specifically, and also give the name
of the worm or virus NAV detects, but it sounds as if you are getting
messages infected with the swen worm. These infected messages are being
sent by computers infected with the swen worm. The swen worm harvests
e-mail addresses from address lists on infected systems AND harvests e-mail
addresses from the headers of posts to newsgroups. If you use your real
e-mail address identity to post to newsgroups (and it appears you do) then
your e-mail address will be harvested, and you will get thousands of e-mails
sent by systems infected by the swen worm. There is little you can do to
stop the flood. Your ISP must begin scanning all e-mail for virus and worm
infections. Blocking senders is of little help since the worm is global.
The worm also uses harvested e-mail addresses on the 'From' line. Below is
information on what the swen worm does.
The 'swen' worm and its effects, particularly on
users with uninfected machines
The flood of e-mail ('swen-mail') is being generated by the 'swen' worm.
Locally, there is not much you can do to stop the flood. Below you will
find a discussion of the effects of the 'swen' worm and ways you can handle
the flood you are getting, even though your machine may not be infected, and
may be well protected.
Only your ISP can stop the flood of 'swen' generated e-mail; by scanning all
e-mail for virus infection.
Until your ISP or e-mail service begins to scan all e-mail for virus
infection, you can use a filter and a program that allows partial
downloading of e-mail messages (Veronica Loell posts information about
these filters quite often; the information is also available at
http://nakawe.sf.net/MMM3.)
Symantec, the publisher of Norton AntiVirus, has a description of the
worm, how to remove it, and removal tools at
http://www.symantec.com/avcenter/venc/data/[email protected] . Other
publishers of antivirus programs have similar webpages. Note well, removing
this worm after your system has been infected is not a simple task.
The 'swen' worm can harvest e-mail addresses from newsgroup postings, so it
is very important to disguise your e-mail identity when posting to Usenet
newsgroups (like microsoft.public.security.virus and tens of thousands of
other active newsgroups .)
"The worm also can search for e-mail addresses in various newsgroups. It
connects to NNTP servers listed in the SWEN1.DAT file, gets a list of all
newsgroups on that server and searches recent messages in these newsgroups
for 'nfrom:' and 'nreply-to:' tags. When such tags are found, the worm gets
e-mail addressed after them and writes them to the GERMS0.DBV file. This way
the worm can harvest a lot of e-mail addresses to send itself to. (From
F-secure,
http://www.f-secure.com/v-descs/swen.shtml )
You can find out how at
http://www.mailmsg.com/SPAM_munging.htm .
This worm has two main effects, and some secondary effects
I. Main effects
A. It infects vulnerable systems and networks.
B. It generates a FLOOD of infected e-mail that is sent to e-mail
addresses it harvests from infected machine and networks. These infected
e-mails are of two types
1. An HTML message that looks like a legitimate Microsoft Security
Bulletin; the hotlinks in this message are valid Microsoft links, and will
even lead you to a description that will allow you to identify this e-mail
as bogus. The message has an attached 104 KByte file that contains the
worm. If you don't have all appropriate Microsoft security patches and
Service Packs installed, it may be possible for your system to be infected
EVEN IF YOU DON'T OPEN THE MESSAGE. So far, the body of this message is
always the same, though the Subject and From lines differ widely. This
message, so far, can be easily be blocked by detecting the string 'Run
attached file' in the body ( in fact, it would be a good practice to
consider ANY e-mail that contains this string AND has an attachment to very,
very likely to carry an infection.
2. A plain text message that purports to be a notification of an
'Undeliverable e-mail', with an attachment that purports to be a copy of the
undeliverable e-mail. This attached file is 104 KBytes long and contains the
worm. The Subject line, From line, and body present in thousands of
combinations, and probably will continue to mutate. Even worse, real e-mail
addresses harvested from infected systems and networks, and from Usenet
newsgroup posts are tagged onto this type of message, causing one of the
secondary effects.
II. Secondary effects
A. Spam effect
1. Mailboxes with an e-mail address that has been harvested from
infected systems, networks and Usenet newsgroup postings begin to be flood
with infected e-mail.
[Personal example: my machines are not infected, but this worm began to
flood my mailbox 17SEP03. I now receive more than 1500 infected e-mail
messages per day. I must empty my mailbox every 5 minutes, 24/7 to avoid
the possibility of having legitimate e-mail bounced. I had to install an
application just to segregate the cleaned, previously infected e-mail
from legitimate e-mail (standard spam blockers can't do this.) There are
filters and programs that can identify this 'swen-mail' and that require
downloading only a portion of an e-mail message to allow discarding or
keeping it based on whether it is
'swen-mail' or not. However, you still must arrange to do this operation
often enough to keep your mailbox from overflowing past the general 10 MByte
limit and bouncing subsequent e-mail. About 80 'swen-mail' messages take up
10 MBytes of storage. If you get 500 'swen-mail messages per day, that
means checking and clearing your mailbox at least every four hours, 24/7, to
insure that no valid e-mail messages are bounced.
B. Notifications from mail services that DO scan for infected
messages, but unfortunately do not realize that the e-mail addresses given
for the sender are either bogus or e-mail addresses harvested by the worm.
Thus, completely innocent mailboxes have insult added to injury.
****
What can you do locally as an individual (i.e. in a SmallOfficeHomeOffice
environment, and /or as a recreational user)?
#1. You can use a remote virus scan from one of the antivirus program
publishers
THEN
#2. You can remove any infections discovered
THEN
#3. You install a good antivirus program, keep it active, keep the virus
definitions up-to-date (at the moment you should update these definitions
EVERY day), and set to scan all incoming e-mails and downloads.
THEN
#4. You can install all appropriate Microsoft security patches and Service
Packs.
THEN
#5. You can consider additional security (DCHP server, firewall, boric acid
[for roaches], .....
If you begin to be flooded with these infected messages, COMPLAIN to your
ISP; send them this URL
http://xtra.co.nz/products/0,,8969,00.html of an ISP that scans incoming
e-mail before passing it to a mailbox. Ask for an increased mailbox size
(if you are getting 1500 of these infected e-mails per day, you will need a
mailbox size over 150 MBytes just to avoid the necessity of completely
emptying it EVERY DAY. Ask about the implicit duty of the ISP to provide
reliable e-mail service, and if they have received notification of any
pending class actions you might join. Ask if they will unbundle their
services so you can opt out of e-mail service and save that cost. That's
about
all you can do about the e-mail flood; only your ISP or other e-mail
provider can come close to solving this problem.
When the e-mail flood becomes too painful, find an ISP or other e-mail
provider that DOES scan and discard infected e-mail before passing it to
your mailbox, and then change to that ISP and/or e-mail provider. Changing
your e-mail address is no solution; as soon as your new e-mail address is
harvested from an infected system or network, the problem starts again.
In the meantime you can use a filter and a program that allows partial
downloading of e-mail messages (Veronica Loell posts information about
these filters quite often; the information is also available at
http://nakawe.sf.net/MMM3 .)
When a mailserver is scanning and not just deleting infected e-mail, but is
also sending an e-mail to notify the sender, write the administrator a nasty
note asking them to stop sending these notices.
****
That's about it; you can proof your system against infection, but only
changes at the mailserver level can stop reception of a flood of infected
e-mails and increasing numbers of inappropriate notices that you've sent
infected e-mail from arriving in your mailbox.
Phil Weldon
--
Phil Weldon, pweldonatmindjumpdotcom
For communication,
replace "at" with the 'at sign'
replace "mindjump" with "mindspring."
replace "dot" with "."
