Trojan.Exprez.B

Posted: June 15, 2012

Threat Metric

The Threat Meter is a malware assessment that SpywareRemove.com's research team is able to give every identifiable malware threat. Our Threat Meter includes several criteria based off of specific malware threats to value their severity, reach and volume. The Threat Meter is able to give you a numerical breakdown of each threat's initial Threat Level, Detection Count, Volume Count, Trend Path and Percentage Impact. The overall ranking of each threat in the Threat Meter is a basic breakdown of how all threats are ranked within our own extensive malware database. The scoring for each specific malware threat can be easily compared to other emerging threats to draw a contrast in its particular severity. The Threat Meter is a useful tool in the endeavor of seeking a solution to remove a threat or pursue additional analytical research for all types of computer users.

The following fields listed on the Threat Meter containing a specific value, are explained in detail below:

Threat Level: The threat level scale goes from 1 to 10 where 10 is the highest level of severity and 1 is the lowest level of severity. Each specific level is relative to the threat's consistent assessed behaviors collected from SpyHunter's risk assessment model.

Detection Count: The collective number of confirmed and suspected cases of a particular malware threat. The detection count is calculated from infected PCs retrieved from diagnostic and scan log reports generated by SpyHunter.

Volume Count: Similar to the detection count, the Volume Count is specifically based on the number of confirmed and suspected threats infecting systems on a daily basis. High volume counts usually represent a popular threat but may or may not have infected a large number of systems. High detection count threats could lay dormant and have a low volume count. Criteria for Volume Count is relative to a daily detection count.

Trend Path: The Trend Path, utilizing an up arrow, down arrow or equal symbol, represents the level of recent movement of a particular threat. Up arrows represent an increase, down arrows represent a decline and the equal symbol represent no change to a threat's recent movement.

% Impact (Last 7 Days): This demonstrates a 7-day period change in the frequency of a malware threat infecting PCs. The percentage impact correlates directly to the current Trend Path to determine a rise or decline in the percentage.

Threat Level:	9/10
Infected PCs:	46

First Seen:	June 15, 2012
OS(es) Affected:	Windows

Trojan.Exprez.B is a recent update to Dorifel, a virus that infects executable files, Word documents and Excel spreadsheets. Other than some enhanced self-distribution capabilities, Trojan.Exprez.B doesn't appear to have any extra features that are currently-functional, although SpywareRemove.com malware experts have noted some instances of Trojan.Exprez.B making contact with URLs that could be a precursor to Trojan.Exprez.B being designed to include downloading or backdoor-related features in the future. Files that are infected by Trojan.Exprez.B can be fully recovered by a combination of dutiful usage of anti-virus software and some minor user effort (such as renaming mislabeled file extensions), and SpywareRemove.com malware experts recommend that you use anti-malware scans for Trojan.Exprez.B's deletion as a matter of course.

Trojan.Exprez.B: When a Small File Change Turns Out to Be a Big Deal

Trojan.Exprez.B is an update to Dorifel or W32/XDocCrypt.a, and keeps the primary functions of these PC threats while adding a few extras on top. The Trojan.Exprez.B update to Dorifel also has been confirmed for compatibility with Windows 7, along with several other versions of that OS (XP, Vista and 2000). Like any virus, Trojan.Exprez.B's foremost function is to propagate itself by adding its own code to unrelated files – in Trojan.Exprez.B's case, EXE, DOCX, DOC, XLS and XLSX files. These files types include the standard executable type for programs, as well as widely-used Microsoft Office formats for Word and Excel. The ability to infect Excel spreadsheets is a recent addition that you can thank Trojan.Exprez.B for including; earlier versions of Dorifel were limited to infecting EXE and Word documents.

Although Trojan.Exprez.B changes a given file type to an .exe (if it isn't already that file type) in the act of infecting it, Trojan.Exprez.B's functions also include capabilities that allow these files to be launched and displayed as normal in their default programs. For example, a Trojan.Exprez.B-infected DOC file would still display normally in Microsoft Word, despite its actual file type being changed to an executable (something that SpywareRemove.com malware experts note can be discerned via the Command Prompt or the 'Type' field of Windows Explorer). Other than these file type changes and some minor file size increases, Trojan.Exprez.B infections don't show obvious symptoms of their attacks.

Future variants of Trojan.Exprez.B may include other features that are related to contacting C&C servers or downloading malicious files, since SpywareRemove.com malware researchers have noted instances of Trojan.Exprez.B using seemingly-harmless image files as an obscure means of contacting malicious URLs without permission.

Scrubbing the Taint of Trojan.Exprez.B Off of Your Hapless Files

Trojan.Exprez.B should be removed with anti-malware products that have a good history against viruses and other file-infecting PC threats. However, any system scans should also be thorough enough to delete other PC threats that are associated with Trojan.Exprez.B, such as its Trojan dropper, Trojan.Exprez.B!gen2. Although files infected by Trojan.Exprez.B are encrypted, the encryption algorithm is a standard one that should be breakable with ease by anti-malware and decryption programs.

Besides its virus-based means of propagation, Trojan.Exprez.B may also be distributed via removable drives (such as USB devices) or networks, just as a worm would be able to infect new PCs. Contact with other PCs should be avoided until you've verified that all of your files are cleansed of Trojan.Exprez.B and related PC threats.

Technical Details

File System Modifications

Tutorials: If you wish to learn how to remove malware components manually, you can read the tutorials on how to find malware, kill unwanted processes, remove malicious DLLs and delete other harmful files. Always be sure to back up your PC before making any changes.

The following files were created in the system:

%UserProfile%\Application Data\Microsoft\[EIGHT RANDOM UPPERCASE CHARACTERS].exe

File name: %UserProfile%\Application Data\Microsoft\[EIGHT RANDOM UPPERCASE CHARACTERS].exe
File type: Executable File
Mime Type: unknown/exe
Group: Malware file

%Windir%\xpsp2res.dll

File name: %Windir%\xpsp2res.dll
File type: Dynamic link library
Mime Type: unknown/dll
Group: Malware file

[ORIGINAL FILE NAME].docx becomes [ORIGINAL FILE NAME]xcod.scr

File name: [ORIGINAL FILE NAME].docx becomes [ORIGINAL FILE NAME]xcod.scr
Mime Type: unknown/scr
Group: Malware file