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roger_grimes
Columnist

Companion worms making it harder to discover malware

Analysis
Oct 15, 20061 min
Data and Information SecuritySecurity

A new series of worms (called Downloader.Agent.awf by some AV products) read infected computer's HKLM (or HKCU) Run keys to find previously installed programs. Then the worm copies the original executable to a new location, and replaces the original copy with a copy of the worm. When the computer executes the Run keys, it runs the worm instead, which then launches the original program. (Malware which renames i

A new series of worms (called Downloader.Agent.awf by some AV products) read infected computer’s HKLM (or HKCU) Run keys to find previously installed programs.

Then the worm copies the original executable to a new location, and replaces the original copy with a copy of the worm. When the computer executes the Run keys, it runs the worm instead, which then launches the original program.

(Malware which renames itself as other legitimate called files are known as spawners, twins, or companions).

This complicates detection and removal process, because the worm will appear as a “known and trusted”, previously installed executable. While this behavior is not new, it’s apparently becoming popular again. So, when looking for malicious code, you cannot simply trust file names and locations. You must verify each file’s integrity hash against a known good copy.

There are many free hash programs available for Windows and Linux. The book ‘PGP and GPG’ turned me onto one for Windows called DigestIT 2004. It like it because it does MD5 and SHA-1 hashs and integrates into Windows as a right-click context menu.

roger_grimes
Columnist

Roger A. Grimes is a contributing editor. Roger holds more than 40 computer certifications and has authored ten books on computer security. He has been fighting malware and malicious hackers since 1987, beginning with disassembling early DOS viruses. He specializes in protecting host computers from hackers and malware, and consults to companies from the Fortune 100 to small businesses. A frequent industry speaker and educator, Roger currently works for KnowBe4 as the Data-Driven Defense Evangelist and is the author of Cryptography Apocalypse.

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