Threat Descriptons



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Aliases :

Typot, Stumbler, Dubbed Stumbler, 55808


Typot is a Linux trojan designed to perform distributed port scanning. One peculiarity of this trojan is that it generates TCP packets with a window size of 55808.


Based on the settings of your F-Secure security product, it will either move the file to the quarantine where it cannot spread or cause harm, or remove it.

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

The only purpose of this trojan is to map open ports on random hosts on the Internet. The way it works suggests that it is an experimental project exploring new ways of port scanning.

Typot is statically linked to two well known libraries:

- 'libnet': library to craft and send network packets
- 'libpcap': network traffic capture library

Using 'libnet' the trojan crafts TCP SYN packet with window size of 55808. Both the source and the destination addresses are random in the packet. This means that even if the port is open on the remote host the response will not go back to the trojan. This feature makes the trojan harder to track down.

To capture the responses from open ports Typot uses the 'libpcap' library. With 'libpcap' the trojan switches the network interface to promiscuous mode and listen to all traffic on the physical network segment. By listening Typot tries to capture responses for TCP SYN requests sent by other instances of the trojan. The collected data is written to a file named 'r' in the same directory where the trojan is located.

The data Typot collects about ports is sent to a predefined IP address by connecting to port 22, every 24 hours. If the specified host is unreachable the trojan unistalls itself by deleting '/tmp/.../a' which is supposedly a copy of it.

Since the trojan is dynamically linked to glibc 2.3 it will work only on recent versions of Linux distributions.

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