When checking System Startup under tools there's an entry for avastUI.exe. That is expected. However, rather than identifying it as a required part of the AVAST virus protection system or even unknown, the description provided says it is "Not required - virus, spyware, malware or other resource hog" [full detail copied below].
I'm running Windows XP with SP3 and microsoft security bug fixes up to november 2011, with Firefox at 3.6.24.
Spybot is with latest detection update 07/Dec/2011
Looking in the View Reports I see the logging:
--- Startup entries list ---
Located: HK_LM:Run, avast
command: "C:\Program Files\AVAST Software\Avast\avastUI.exe" /nogui
file: C:\Program Files\AVAST Software\Avast\avastUI.exe
size: 3744552
MD5: F7226AA410954185160067D5FA82F3F2

Please advise if any further detail is required to sort out this problem.
Current filename: "C:\Program Files\AVAST Software\Avast\avastUI.exe" /nogui

Database status: Not required - virus, spyware, malware or other resource hog
Value: avast
Filename: troyan.exe

Added by the _SMALL.CZ_ TROJAN!

Source: Paul Collins Startup list