Summary
Carrytone is a mass-mailer that uses a new technique to spread. The worm body is 40 kilobytes in size and it was written in C. It works properly on Windows NT based systems only.
Removal
1. The extra registry keys/values must be removed first from
'[HKLM]\Software\Microsoft\Windows\CurrentVersion\Run\mmopl' '[HKLM]\Software\Microsoft\Media Optimization Library'
2. When the registry is clean the system has to be rebooted to make sure that the worm process is not active anymore. After the reboot the worm can be deleted from the Windows directory; it is called 'MMOPLIB.EXE'.
3. The hosts file has to be cleaned. The file is called '%system_dir%\drivers\etc\hosts'. All the extra mailserver addresses must be removed that point to the localhost (127.0.0.1).
A False Positive is when a file is incorrectly detected as harmful, usually because its code or behavior resembles known harmful programs. A False Positive will usually be fixed in a subsequent database update without any action needed on your part. If you wish, you may also:
Check for the latest database updates
First, check if your F-Secure security program is using the latest updates, then try scanning the file again.
Submit a sample
After checking, if you still believe the file is incorrectly detected, you can submit a sample of it for re-analysis.
Note: If the file was moved to quarantine, you need to collect the file from quarantine before you can submit it.
Exclude a file from further scanning
If you are certain that the file is safe and want to continue using it, you can exclude it from further scanning by the F-Secure security product.
Note: You need administrative rights to change the settings.
Technical Details
For spreading it implements a simple SMTP proxy that listens on port 25 (standard SMTP port) on the infected machine. When the worm is started it fetches the SMTP server name from the user's email settings then it modifies the HOSTS file so that the SMTP server's address points to the localhost where the worm is listening. This way when the user sends an email his/her email client will connect to the worm instead of the real mail server. After receiving the connection the worm relays all the commands and replies between the client and the real mail server until it gets the reply to SMTP DATA command that marks the beginning of the email data. At this point it inserts a copy of itself into the message.
The attachment name it uses is composed from the recipient's name and a '.doc.pif' extension.
Messages look like this:
When the infected attachment is opened it copies itself to the Windows folder as 'MMOPLIB.EXE' and adds it to the runkeys in the registry:
- '[HKLM]\Software\Microsoft\Windows\CurrentVersion\Run\mmopl'
The worm stores some internal data under
- '[HKLM]\Software\Microsoft\Media Optimization Library'
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