A mass-mailer, also called an Internet worm, is usually a
standalone program that sends itself as an e-mail attachment to
e-mail addresses that it could find on an infected computer. Mass
mailers became very widespread in the beginning of 21st century.
Most of the malware nowdays are mass-mailers.
Typically a mass mailer arrives on a computer with an infected
e-mail message. In some cases an infected attachment of such
message can start automatically, in other cases a user has to run
an attachment to become infected. When a typical mass-mailer is
activated, it installs itself to system by copying its file into
Windows or Windows System folder, creates a startup key for its
file in the Registry or modifies WIN.INI or SYSTEM.INI file and
stays active in memory. While active, a mass mailer collects
e-mail addresses from user's Address Book or searches for
specific files (for example for HTML files) and tries to locate
e-mail addresses there. Finally a mass mailer connects to any
available SMTP server (usually a default user's SMTP server is
used) and sends itself to all or a few selected found e-mail
addresses.
Some mass mailers randomly compose subjects and bodies of
infected messages from words and phrases that they have in their
bodies. Some worms use contents of randomly found files as e-mail
message's body or subject. Worm's attachment names could be
either random, or 'borrowed' from other files.
Many worms send themselves as attachments with double extension,
for example .MPG.EXE or AVI.PIF. In this case a recipient in most
cases can only see the first extension. Because of that some
users try to start such attachments thinking that these are
multimedia files.
It has become a tradition to create complex worms that carry
viruses and backdoors inside them or that have additional
features like local network spreading or password or data
stealing.
Also the latest worms try to disable anti-virus and security
software on infected computers. Some worms attempt to steal data
by attaching images or document files to infected messages that
they send out. A few worms have destructive payload and destroy
an infected system after they send themselves out.
Most famous mass mailers: Klez, Nimda, Yaha, Sircam, Bugbear,
Magistr, Braid, Badtrans, PrettyPark, Sobig.
Disinfection
Automatic Disinfection
Usually standalone malware (backdoors, worms, trojans, etc.) is
automatically removed by F-Secure Anti-Virus (FSAV) starting from
version 5.40. Malware files get automatically renamed by FSAV, so
they can not be started any more. In some rare cases, when
automatic disinfection is not possible, a user can select
disinfection action by him/herself to make FSAV rename or delete
an infected file. In some special cases it is recommended to use
specific disinfection tools provided by F-Secure. They can be
downloaded from our ftp site:
F-Secure Anti-Virus can be purchased from our webshop or from our
authorised distributors. A trial version F-Secure Anti-Virus,
limited to 30 days, can be downloaded from our website:
All the latest versions of FSAV can download anti-virus database
updates automatically. However, these updates can be also
downloaded and installed manually from our web or ftp sites:
To manually disinfect standalone malware (backdoors, worms,
trojans, etc.) it's usually enough to delete all infected files
from a computer and to restart it. Active malware files are
usually locked by operating system so different disinfection
approaches are required for different operating systems.
Please note that manual disinfection is a risky process, so it is
recommended only for advanced users.
Windows 95, 98, ME
If Windows 9x operating system is used, it is recommended to
restart a computer from a bootable system diskette and to delete
an infected file from command prompt. For example if a malicious
file named ABC.EXE is located in Windows folder, it is usually
enough to type the following command at command prompt:
DEL C:\WINDOWS\ABC.EXE
and to press Enter. After that an infected file will be gone.
Windows NT, 2000, XP
If Windows NT, 2000 or XP is used, a malicious file has to be
renamed with a different extension (for example .VIR) and then a
system has to be restarted. After restart a renamed malicious
file will no longer be active and it can be easily deleted
manually.
System Restore issue
If Windows ME or XP is used, it is recommended to disable System
Restore feature of these operating systems to prevent a computer
from re-infection by an already removed malware. The fact is that
System Restore feature of these operating systems might save an
infected file into the special folder and copy it back to a hard
drive it every time it's been renamed or deleted by F-Secure
Anti-Virus or by a user. Instructions on how to disable System
Restore feature are here:
It is recommended to re-enable System Restore after disinfection
in order to restore stable system configuration in the future,
if any crash or incompatibility issue occurs.
Contacting F-Secure for help
If you have problems with disinfection, please consult a computer
technician or send a message (and a sample) to our Viruslab. We
have guidelines for sending virus samples, hoaxes and
virus-related questions to F-Secure Viruslab published here:
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