Yarner is a Windows PE EXE file about 434K in size, written in Delphi. It uses its own e-mail engine to send copies of itself to others.
Once executed, the worm deletes the Windows directory on infected computers.
At present, the infections are limited to Germany. However, a new variation could be produced in English or any other language.
Because of the dangerous potential of this worm, Yarner ranks a seven on the ZDNet Virus Meter.
What it does
Yarner arrives by e-mail and appears to be from Trojaner-Info [webmaster@trojaner-info.de]. This is a real address and is not the true origin of this e-mail.
The subject of the infected e-mail reads "Trojaner-Info Newsletter [Current Date]". The body text is in German and appears to be a newsletter.
The attached file with this e-mail is yawsetup.exe. If executed, Yarner will copy itself to the Windows directory as notedpad.exe, overwriting the system's original Notepad application (notepad.exe). Whenever you launch Notepad, Yarner uses notedpad.exe to hide its presence. The worm adds two additional files: kerneI32.daa (which the worm uses to write e-mails) and kerneI32.das (which the worm uses to write known SMTP).
The worm then changes this registry file:
HKCUSoftwareMicrosoftWindowsCurrentVersionRunonce [random characters] = [random characters].exe
There can be up to 100 random characters assigned to these values.
To send e-mail, Yarner gains access to the Microsoft Outlook address book then scans all .php, .htm, .shtm, .cgi, .pl files in all subdirectories, looking for additional e-mail addresses. Yarner then uses its own SMTP engine (e-mail program) to send e-mails and connects to its own list of servers, including:
216.113.14.106 joy-go.gr.jp ctripserver.ctrip.com.cn 202.101.62.207 cocess.cocess.co.kr mail.bizpoint.com.sg ns2.webshock.co.kr olympus.mda.com.tr linux2.ele-china.com mailsvr.hanace.co.kr
After it has sent copies of itself, Yarner then deletes all files in the Windows directory.
Prevention
Users of Microsoft Outlook 2002 and users of Outlook 2000 who have installed the Security Update should be safe from opening the attached file with Yarner.
Users who have not upgraded to Outlook 2002 or who have not installed the Security Update for Outlook 2000 should do so.
In general, do not open attached files in e-mail without first saving them to hard disk and scanning them with updated antivirus software. Contact your antivirus vendor to obtain the most current antivirus signature files that include Yarner.
Removal
Almost all the antivirus software companies have updated their signature files to include this worm. This will stop the infection upon contact and in some cases will remove an active infection from your system. For more information, see Central Command, F-Secure, Kaspersky, McAfee, Norman, Sophos, Symantec, and Trend Micro.
