Classification

Category: Malware

Type: Worm

Aliases: Sonic, I_Worm_Sonic, I-Worm.Sonic, Sonic.b

Summary


This is multi-component Internet worm infecting Win32 machines and spreading itself in email messages as attached EXE file. The worm has several components and is able to 'upgrade' itself from an Internet Web site.

Removal


Automatic action

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Technical Details


There are two principal worm components: Loader and Main component.

The Loader is Windows EXE file about 25K of size (it is compressed by UPX PE EXE files compression utility, being decompressed it gets about 70K of size). When loader is activated on a computer (being run from email attach) it registers itself as a hidden process (service), copies itself to Windows system directory with GDI32.EXE name and registers in auto-run system registry key:

HKLM\Software\Microsoft\Windows\CurrentVersion\Run
 GDI = WinSystem\GDI32.EXE

where 'WinSystem' is Windows system directory name. As a result the worm Loader then will be executed on each Windows startup. Note that there are standard Windows components in that directory: GDI.EXE and GDI32.DLL. The worm uses GDI32.EXE name to disguise itself in a standard Windows environment.

To hide its activity the worm then displays the fake error message:

The path in the above message may be different.

The worm then activates main procedure that gets and executes the Main component. It contacts GeoCities Website and gets several files from one of accounts there:

LASTVERSION.TXT - a text file with the number of latest worm version
available in there. If there is no new version, the worm
exits.
nn.ZIP

- latest version of worm Main component, "nn" is
defined in LASTVERSION.TXT.
GATEWAY.ZIP

 - latest version of worm Loader component.

The nn.ZIP and GATEWAY.ZIP files actually are not archives, but encrypted Windows EXE file. The worm Loader decrypts them, copies to Windows directory and spawns. As a result the Main component is activated on the computer.

The Main worm component is Windows EXE file about 40K of size (it is compressed by UPX PE EXE files compression utility, being decompressed it gets about 120K of size). It is installed to Windows directory with GDI32A.EXE name and is registered in system registry in similar way as described above for virus loader. The main components then depending on some conditions opens Windows Address Book, gets Inet addresses from there and sends infected email messages. In known worm version these messages have:

Subject: Choose your poison
Attached file name: GIRLS.EXE

The B variant of the worm spreads itself a bit differently:

Subject: I'm your poison
Attached file name: LOVERS.EXE

The Main worm component also has backdoor abilities. It can provide a limited access to an infected computer for a remote hacker.