Threat Encyclopedia

Selected viruses, spyware, and other threats: sorted alphabetically


MyTob.CH is a typical mass mailing e-mail worm, the size is 44544 bytes and the worm is runtime compressed by PESpin.

Installation and Autostart Techniques

Upon execution, the worm copies itself into the System32 folder as "LienVandeKelder.exe".

The worm creates a mutex "H-3-l-l-B-0-t-3!!!" to avoid multiple running instances of the worm on one machine.

The worm adds the following registry keys to the registry to make sure that it runs every time windows is started:

"" = "LienVandeKelder.exe"

"" = "LienVandeKelder.exe"

MyTob.CH also adds the following registry key:

"Start" = "4"

The worm tries to terminate several programs:


E-mail harvesting

The worm scans all fixed disks and collects e-mail addresses out of files which match one of the following file extensions:

*.wab, *.adb, *.tbb, *.dbx, *.asp, *.php, *.sht, *.htm, *.pl

However, these extensions are pretty much useless, because the worm has a bug regarding stringcat and compare with the WIN32_FIND_DATA results.

That said: The worm will always open and scan a file for email addresses when at least one character matches one of the characters in the file extension list in the correct order.
In technical terms, that means the worm compares the file extension via 'instring function/substring function'.

Example: The worm will search for e-mail addresses in files where the file extension matches *.htm, *.ht, *.h for instance.

Note: Mytob.CH collects also e-mail addresses from the Windows Address Book and from the following folders:

%Windir%\Temporary Internet Files
%Userprofile%\Local Settings\Temporary Internet Files

DNS resolving

The worm performs DNS e-mail-exchange-queries to find an appropriate mail server for each domain it tries to send itself to. If this DNS request for the mailserver fails, the worm tries to guess the e-mail server adding in front of the domain name the following prefixes:

gate. mx. mail. smtp. mx1. mxs. mail1. relay. ns.

E-mail Sender

The worm generates the sender's e-mail addresses using the following list of names:

adam, alex, alice, andrew, anna, bill, bob, brenda, brent, brian, britney, bush, claudia, dan, dave, david, debby, fred, george, helen, jack, james, jane, jerry, jim, jimmy, joe, john, jose, julie, kevin, leo, linda, lolita, madmax, maria, mary, matt, michael, mike, peter, ray, robert, sam, sandra, serg, smith, stan, steve, ted, tom

at which it adds randomly, domain names (the domain names are encrypted and stored in the worm):

It uses its own SMTP (Simple Mail Transfer Protocol) engine to mass-mail copies of itself to other e-mail addresses.

E-mail subjects

MyTob.CH selects randomly an eMail subject out of the following list:

Notice: **Last Warning**
Your email account access is restricted
Your Email Account is Suspended For Security Reasons
Notice:***Your email account will be suspended***
Security measures
Email Account Suspension
*IMPORTANT* Please Validate Your Email Account
*IMPORTANT* Your Account Has Been Locked

 Note: The e-mail subjects are encrypted and stored in the worm.

Message Body

The e-mail contains one of the following message texts:

Once you have completed the form in the attached file , your account records will not be interrupted and will continue as normal.
To unblock your email account acces, please see the attachment.
Follow the instructions in the attchment.
We have suspended some of your email services, to resolve the problem you should read the attached document.
To safeguard your email account from possible termination, please see the attached file.
please look at attached document.
Account Information Are Attached!

 Note: The worm may also send e-mails containing a blank message body or random strings.

E-mail Attachments

The worm attaches one of the following file names with a self-copy:


with one of the following file extensions:


The worm may also attach itself as a ZIP file. The file inside the ZIP archive may have two extensions, the first chosen from the following list:


 The second extension is chosen from the following list and is separated from the first extension by a huge amount of spaces to hide the executable file extension:


Example: attachment "" may contain the file "text.txt { spaces }.scr"

 The worm avoids e-mail addresses which contain parts of the following list:

.gov, .mil, abuse, accoun, acketst, admin, anyone, arin., avp, be_loyal:, berkeley, borlan, bsd, bugs, certific, contact, example, fcnz, feste, fido, foo., fsf., gnu, gold-certs, google, gov., help, hotmail, iana,, icrosof, icrosoft, ietf, info, inpris, isc.o, isi.e, kernel, linux, listserv, math, mit.e, mozilla, msn., mydomai, nobody, nodomai, noone, not, nothing, ntivi, page, panda, pgp, postmaster, privacy, rating, rfc-ed, ripe., root, ruslis, samples, secur, sendmail, service, site, soft, somebody, someone, sopho, spm, submit, support, syma, tanford.e, the.bat, unix, usenet, utgers.ed, webmaster, www, you, your, -._!, -._!@

Note: The first missing character should match, for instance, "Microsoft" as well as "microsoft". The worm will not send emails to addresses which containing one of the following strings:

Hostmaster, Support, Administrator, Mail, Service, Admin, Info, Staff, Register, Validation, Webmaster

Hostfile Manipulation

It overwrites the present host's file with the following data to avoid accessing these sites:

Other Details:

The worm also provides IRC-Backdoor functionality with the following functions:

Downloading files
Downloading new worm updates
Executing files
Providing uptime information to the remote controller
Providing information about the worm variant to the remote controller
Notifying IRC Channels/Operator via private message
Restarting the computer

It tries to connect to the irc server