Is ClamWin itself infected?
It happened to 2 of my USB sticks after they were updated via internet (as per ClamWin) from 2 different XP machines!

Scan Started Mon Dec 22 15:13:34 2008
-------------------------------------------------------------------------------

*** Scanning Programs in Computer Memory ***
*** Memory Scan: using ToolHelp ***

Unloading program E:\PortableApps\ClamWinPortable\ClamWinPortable.exe from memory

*** Scanned 30 processes - 389 modules ***
*** Computer Memory Scan Completed ***


E:\PortableApps\ClamWinPortable\ClamWinPortable.exe: Trojan.Agent-65355 FOUND
----------- SCAN SUMMARY -----------
Known viruses: 478292
Engine version: 0.94.1
Scanned directories: 0
Scanned files: 419
Infected files: 1

Data scanned: 168.95 MB
Time: 155.543 sec (2 m 35 s)
--------------------------------------
Completed
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It could be that Clamwin didn't have that trojan signature in its database until the latest update. Also, see the previous post on how to verify whether a file is infected and what to do if it is a false positive.

Regards,

Thank you GuitarBob for your prompt & accurate response!

As per your suggestion, I submitted ClamWinPortable.exe to Jotti's & Virus Total; only ClamAV reported positive. It is most likely a false positive. I have also submitted the file and finding to ClamAV.

Best regards!