The worm's body is a Windows PE executable file compressed with the MEW executable compressor and was patched by PE_Patch utility.
When the worm's file is run, it copies itself to Windows System Folder with a random name ending in '32.exe' (for example pmbperim32.exe) and creates a startup key for this file in the Registry:
"Rhino" = "%SystemDir%\[randomname]32.exe"
where "%SystemDir%" represents the Windows System folder name, for example "C:\Windows\System32\" on Windows XP systems.
To gather email addresses Bofra.A searches the Windows Address Book, files in Temporary Internet File and other files on the hard disk that have the following strings in their name:
Using its own SMTP engine Bofra.A sends emails to the collected addresses. Sender of the mails is spoofed and the content is randomly chosen from the following components:
funny photos :)
Email bodies contain an HTML-formatted text:
FREE ADULT VIDEO! SIGN UP NOW!
Look at my homepage with my last webcam photos!
The email does not have any attachments. The worm only sends the link which points to the infected host. The format of the link is
https://[infected host ip]:port/[file_to_dowload]
Bofra.A, running on the infected host, has a stripped-down web servers listening on TCP ports starting from 1638 (0x666). The only purpose of these is to serve the potential targets with the HTML page that contains the exploit as well as the worm executable that the exploit will download.
The way this propagation technique works in explained in our weblog:
The emails sent by Bofra.A contain a fake virus scanner header (X-AntiVirus:) that might get one of the following values:
scanned for viruses by AMaViS 0.2.1 (http://amavis.org/)
Checked for viruses by Gordano's AntiVirus Software
Checked by Dr.Web (http://www.drweb.net)
The worm avoids posting to email addresses that contain certain strings:
The worm fakes the sender's address. It uses the following list of names to compose the fake address:
The worm uses the following list of domain names to compose the fake sender's address:
As a payload Bofra.A has an IRC-controlled backdoor that allows the worm's author to download and execute arbitrary programs on the compromised host.