Ciao Alfonso e grazie.
Ho fatta la scansione antivirus in modalità provvisoria ed è risultata uguale all'altra.
Poi ho fatto questo che ti spedisco.
Saluti Renato

Logfile of HijackThis v1.99.1
Scan saved at 12.37.53, on 21/03/2005
Platform: Windows XP SP2 (WinNT 5.01.2600)
MSIE: Internet Explorer v6.00 SP2 (6.00.2900.2180)

Running processes:
C:\WINDOWS\System32\smss.exe
C:\WINDOWS\system32\winlogon.exe
C:\WINDOWS\system32\services.exe
C:\WINDOWS\system32\lsass.exe
C:\WINDOWS\System32\Ati2evxx.exe
C:\WINDOWS\system32\svchost.exe
C:\WINDOWS\System32\svchost.exe
C:\WINDOWS\system32\LEXBCES.EXE
C:\WINDOWS\system32\LEXPPS.EXE
C:\WINDOWS\system32\spoolsv.exe
C:\WINDOWS\system32\Ati2evxx.exe
C:\WINDOWS\Explorer.EXE
C:\WINDOWS\system32\RunDll32.exe
C:\Programmi\File comuni\Symantec Shared\ccApp.exe
C:\Programmi\Lexmark X6100 Series\lxbfbmgr.exe
C:\PROGRA~1\PHILIP~1\VProperty.exe
C:\WINDOWS\Dit.exe
C:\WINDOWS\system32\ctfmon.exe
C:\Programmi\Lexmark X6100 Series\lxbfbmon.exe
C:\Programmi\File comuni\Symantec Shared\ccProxy.exe
C:\Programmi\File comuni\Symantec Shared\ccSetMgr.exe
C:\Programmi\Norton AntiVirus\navapsvc.exe
C:\Programmi\File comuni\Symantec Shared\SNDSrvc.exe
C:\WINDOWS\System32\svchost.exe
C:\Programmi\File comuni\Symantec Shared\ccEvtMgr.exe
C:\Programmi\File comuni\Symantec Shared\Security Center\SymWSC.exe
C:\Programmi\Norton AntiVirus\SAVScan.exe
C:\Programmi\Internet Explorer\iexplore.exe
C:\Programmi\Messenger\msmsgs.exe
C:\DOCUME~1\Renato\IMPOST~1\Temp\Directory temporanea 1 per hijackthis.zip\HijackThis.exe

R0 - HKCU\Software\Microsoft\Internet Explorer\Main,Start Page = http://www.virgilio.it/home/index_nf.html
R0 - HKCU\Software\Microsoft\Internet Explorer\Main,Local Page =
R0 - HKLM\Software\Microsoft\Internet Explorer\Main,Local Page =
R0 - HKCU\Software\Microsoft\Internet Explorer\Toolbar,LinksFolderName = Collegamenti
O2 - BHO: AcroIEHlprObj Class - {06849E9F-C8D7-4D59-B87D-784B7D6BE0B3} - C:\Programmi\Adobe\Acrobat 5.0\Reader\ActiveX\AcroIEHelper.ocx
O2 - BHO: (no name) - {53707962-6F74-2D53-2644-206D7942484F} - C:\PROGRA~1\SPYBOT~1\SDHelper.dll
O2 - BHO: Web assistant - {9ECB9560-04F9-4bbc-943D-298DDF1699E1} - C:\Programmi\File comuni\Symantec Shared\AdBlocking\NISShExt.dll
O2 - BHO: NAV Helper - {BDF3E430-B101-42AD-A544-FADC6B084872} - C:\Programmi\Norton AntiVirus\NavShExt.dll
O3 - Toolbar: Norton AntiVirus - {42CDD1BF-3FFB-4238-8AD1-7859DF00B1D6} - C:\Programmi\Norton AntiVirus\NavShExt.dll
O3 - Toolbar: Web assistant - {0B53EAC3-8D69-4b9e-9B19-A37C9A5676A7} - C:\Programmi\File comuni\Symantec Shared\AdBlocking\NISShExt.dll
O4 - HKLM\..\Run: [Cmaudio] RunDll32 cmicnfg.cpl,CMICtrlWnd
O4 - HKLM\..\Run: [SplashDisplayer] C:\WINDOWS\System32\ISTHTB.EXE
O4 - HKLM\..\Run: [ccApp] "C:\Programmi\File comuni\Symantec Shared\ccApp.exe"
O4 - HKLM\..\Run: [Yahoo Update] Yahoo.exe
O4 - HKLM\..\Run: [Symantec NetDriver Monitor] C:\PROGRA~1\SYMNET~1\SNDMon.exe
O4 - HKLM\..\Run: [NeroFilterCheck] C:\WINDOWS\system32\NeroCheck.exe
O4 - HKLM\..\Run: [Lexmark X6100 Series] "C:\Programmi\Lexmark X6100 Series\lxbfbmgr.exe"
O4 - HKLM\..\Run: [QuickTime Task] "C:\Programmi\QuickTime\qttask.exe" -atboottime
O4 - HKLM\..\Run: [ToUcamVProperty] C:\PROGRA~1\PHILIP~1\VProperty.exe
O4 - HKLM\..\Run: [Dit] Dit.exe
O4 - HKLM\..\Run: [URLLSTCK.exe] C:\Programmi\Norton Internet Security\UrlLstCk.exe
O4 - HKLM\..\RunServices: [Yahoo Update] Yahoo.exe
O4 - HKCU\..\Run: [CTFMON.EXE] C:\WINDOWS\system32\ctfmon.exe
O4 - HKCU\..\Run: [Yahoo Update] Yahoo.exe
O4 - HKCU\..\Run: [NBJ] "C:\Programmi\Ahead\Nero BackItUp\NBJ.exe"
O4 - Global Startup: Adobe Gamma Loader.lnk = C:\Programmi\File comuni\Adobe\Calibration\Adobe Gamma Loader.exe
O8 - Extra context menu item: Open using &Advanced JPEG Compressor - C:\Programmi\Advanced JPEG Compressor\ajcieex.htm
O9 - Extra button: Messenger - {FB5F1910-F110-11d2-BB9E-00C04F795683} - C:\Programmi\Messenger\msmsgs.exe
O9 - Extra 'Tools' menuitem: Windows Messenger - {FB5F1910-F110-11d2-BB9E-00C04F795683} - C:\Programmi\Messenger\msmsgs.exe
O9 - Extra button: Trashcan - {072F3B8A-2DA2-40e2-B841-88899F240200} - C:\WINDOWS\System32\shdocvw.dll (HKCU)
O9 - Extra 'Tools' menuitem: Show Trashcan - {072F3B8A-2DA2-40e2-B841-88899F240200} - C:\WINDOWS\System32\shdocvw.dll (HKCU)
O16 - DPF: ImageUploader - http://fotoalbum1.aruba.it/admin/ImageUploader.CAB
O17 - HKLM\System\CCS\Services\Tcpip\..\{4977776B-EB8C-40B9-B3DE-01151076C821}: NameServer = 85.37.17.14 151.99.125.1
O17 - HKLM\System\CS1\Services\Tcpip\..\{4977776B-EB8C-40B9-B3DE-01151076C821}: NameServer = 85.37.17.14 151.99.125.1
O23 - Service: Ati HotKey Poller - Unknown owner - C:\WINDOWS\System32\Ati2evxx.exe
O23 - Service: ATI Smart - Unknown owner - C:\WINDOWS\system32\ati2sgag.exe
O23 - Service: Symantec Event Manager (ccEvtMgr) - Symantec Corporation - C:\Programmi\File comuni\Symantec Shared\ccEvtMgr.exe
O23 - Service: Symantec Network Proxy (ccProxy) - Symantec Corporation - C:\Programmi\File comuni\Symantec Shared\ccProxy.exe
O23 - Service: Symantec Password Validation (ccPwdSvc) - Symantec Corporation - C:\Programmi\File comuni\Symantec Shared\ccPwdSvc.exe
O23 - Service: Symantec Settings Manager (ccSetMgr) - Symantec Corporation - C:\Programmi\File comuni\Symantec Shared\ccSetMgr.exe
O23 - Service: LexBce Server (LexBceS) - Lexmark International, Inc. - C:\WINDOWS\system32\LEXBCES.EXE
O23 - Service: Servizio Norton AntiVirus Auto-Protect (navapsvc) - Symantec Corporation - C:\Programmi\Norton AntiVirus\navapsvc.exe
O23 - Service: SAVScan - Symantec Corporation - C:\Programmi\Norton AntiVirus\SAVScan.exe
O23 - Service: ScriptBlocking Service (SBService) - Symantec Corporation - C:\PROGRA~1\FILECO~1\SYMANT~1\SCRIPT~1\SBServ.exe
O23 - Service: Symantec Network Drivers Service (SNDSrvc) - Symantec Corporation - C:\Programmi\File comuni\Symantec Shared\SNDSrvc.exe
O23 - Service: Sony SPTI Service (SPTISRV) - Sony Corporation - C:\Programmi\File comuni\Sony Shared\AVLib\Sptisrv.exe
O23 - Service: SymWMI Service (SymWSC) - Symantec Corporation - C:\Programmi\File comuni\Symantec Shared\Security Center\SymWSC.exe

Ciao Alfonso, come da tue istruzioni ho fatto tutto. Però con il mio antivirus mi rileva sempre questo file "C:\WINDOWS\Downloaded Program Files\SAHUninstall_.exe". Con quello in linea invece mi rileva questi "C:\WINDOWS\Downloaded Program Files\lsp_.dll è infettato con Adware.SAHAgent C:\WINDOWS\Downloaded Program Files\SAHAgent_.exe è infettato con Adware.SAHAgent C:\WINDOWS\Downloaded Program Files\SahHtml_.exe è infettato con Adware.SAHAgent C:\WINDOWS\Downloaded Program Files\SAHUninstall_.exe è infettato con Adware.SAHAgent C:\temp\sahagent.exe è infettato con Adware.SAHAgent" dei quali ho trovato solo l'ultimo e quindi eliminato.
Ora se mi puoi consigliare cosa posso ancora fare. Faccio presente però, che oltre alla visione dei file infetti, nel computer non noto alcuna anomalia.
Saluti e grazie. Renato