We got several reports about the 'Small.avu' trojan downloader on May 24th, 2005. According to those reports the trojan was spammed to a large number of people in e-mail messages. The trojan downloader is programmed to download and run a Dumador backdoor variant from a website.
Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.
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The trojan downloader's file is a PE executable 1648 bytes long, packed with FSG file compressor.
According to the reports the trojan downloader was spammed with e-mail messages that looked like that:
ISTE RUS CITIRLAR
SELAM BEYLER!!!! NATASHALAR SIZLERI BEKLIYOR::::.. HERZAMAN BIR RUSYALI NATASHA ILE SEX DOLU BIR GECE YASAMAYI HEPINIZ DUSUNMUSSUNUZDUR.ISTE FIRSAT.BU GERCEKLESEBILIR,YUZLERCE RUS KIZI TURKIYEYE GELMEK ICIN SIZLERI BEKLIYOR.7/24 SIZINLE VE EMRINIZDE. MAILIMIZDE KIZLARIMIZIN RESIMLERINI GOREBILIRSINIZ.BEGENIN,SECIN.VE SIZIN OLSUN. GERISI SIZE KALMIS:::.
The trojan downloader's file was attached to these messages as 'ATTACH.RAR.EXE' file. When this file is run by a user, it attempts to download and run a variant of Dumador backdoor from the following website:
We have reported the abuse to the ISP that hosts that website.
The downloaded Dumador backdoor variant is detected as 'Backdoor.Win32.Dumador.bl'
with the following F-Secure Anti-Virus update:
Detection Type: PC
The trojan downloader is detected as 'W32/Small.avu' with the following F-Secure Anti-Virus
Detection Type: PC
Description Details: Alexey Podrezov, May 24th, 2005