Virus Profile: Medfos.a

Threat Search
Virus Profile information details
Risk Assessment: Home Low | Corporate Low
Date Discovered: 4/27/2012
Date Added: 4/27/2012
Origin: N/A
Length: Varies
Type: Trojan
Subtype: Win32
DAT Required: 6694
Removal Instructions


This is a Trojan detection. Unlike viruses, Trojans do not self-replicate. They are spread manually, often under the premise that they are beneficial or wanted. The most common installation methods involve system or security exploitation, and unsuspecting users manually executing unknown programs. Distribution channels include email, malicious or hacked web pages, Internet Relay Chat (IRC), peer-to-peer networks, etc.


  • Kaspersky -
  • Microsoft   - Trojan:Win32/Medfos.A
  • Sophos     - Mal/EncPk-ZC

Indication of Infection

  • Presence of aforementioned file and registry keys.
  • Network activity with servers mentioned above.

Methods of Infection

Trojans do not self-replicate. They are spread manually, often under the premise that the executable is something beneficial. Distribution channels include IRC, peer-to-peer networks, newsgroup postings, email spam, etc.

Virus Characteristics

Upon execution, the Trojan drops the following file.

  • %Temp%\prnemg.dll

The following registry key has been added to the system

  • [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\]
    “prnemg” = "rundll32.exe "%Temp%\prnemg.dll",SetSaveResolution"

The above mentioned registry entry confirms that the Trojan executes every time when windows starts.

Communicates with a remote host

Medfos.A connects to various remote servers using HTTP protocol (port 80) and attempts to download arbitrary files. The trojan was observed to contact domains with the following suffixes:

  • [Removed].com
  • [
  • [Removed].net

All Users:
Use current engine and DAT files for detection and removal.

Modifications made to the system Registry and/or INI files for the purposes of hooking system startup, will be successfully removed if cleaning with the recommended engine and DAT combination (or higher).


PC Infected? Get Expert Help

Virus Removal Service

Connect to one of our Security Experts by phone. Have your PC fixed remotely - while you watch!