Win95_Caw

Classification

Win95.Caw

Summary

Caw is a dangerous memory resident Win95/98 virus. When an infected program is run the virus gets control, switches itself from application level (Ring3) to Windows kernel (Ring0), allocates a block of Windows memory, hooks file access functions (IFS API) and stays memory resident as a system VxD driver. The virus then intercepts file opening function and writes itself to the end of PE EXE files that are opened. While infecting a file the virus increases last file section and writes itself to there.

Removal

Based on the settings of your F-Secure security product, it will either move the file to the quarantine where it cannot spread or cause harm, or remove it.

A False Positive is when a file is incorrectly detected as harmful, usually because its code or behavior resembles known harmful programs. A False Positive will usually be fixed in a subsequent database update without any action needed on your part. If you wish, you may also:

Check for the latest database updates
First check if your F-Secure security program is using the latest updates, then try scanning the file again.
Submit a sample
After checking, if you still believe the file is incorrectly detected, you can submit a sample of it for re-analysis.
Note: If the file was moved to quarantine, you need to collect the file from quarantine before you can submit it.
Exclude a file from further scanning
If you are certain that the file is safe and want to continue using it, you can exclude it from further scanning by the F-Secure security product.
Note: You need administrative rights to change the settings.

Technical Details

The virus has a bug and in some cases corrupts files while infecting them. When such files are run they cause a standard Windows message about error in application to appear.

The virus has two dangerous payloads. 1s: on 7th of July on each file opening the virus erases 16 sectors at random position on the drive C:.

If current minutes are equal to 0 the virus deletes the files that are being opened: WINWORD.EXE, and files with extensions:

 BMP JPG DOC WRI BAS SAV PDF RTF TXT

The second payload can be 'customized': if there is the file called 'C:\AW' the virus gets file names and extensions from this file, and deletes them.