salve ancora. Ho eseguito le operazioni indicate, ma il problema persiste. L'antivirus continua a non rilevare niente, ma spybot mi segnala sempre il problema (anche se ho eliminato il file). In particolare questo riguarda tre chiavi di registro. La prima mi viene indicata sotto la voce Microsoft.Windows Security Center_disabled e rigurda la chiave: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services|wscsvc\Start!=W=2. Spybot riesce a cancellarla, ma ogni tanto ricompare.
Le altre due riguardano, invece la voce LSA e sono: HKEY_USERS\S-1-5-18\SYSTEM\CurrentControlSet\Control\Lsa a cui sono associati due valori uno predefinito non impostato e il secondo Win Net Wks32 con valore netwks32.exe
HKEY_USERS\.Default\SYSTEM\CurrentControlSet\Control\Lsa on gli stessi valori di prima.

Questo, invece, è il log di Hijack fatto dopo le operazioni indicatemi:
Logfile of HijackThis v1.99.1
Scan saved at 20.45.25, on 13/09/2006
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\svchost.exe
C:\WINDOWS\System32\svchost.exe
C:\WINDOWS\system32\spoolsv.exe
C:\WINDOWS\System32\svchost.exe
C:\WINDOWS\system32\ZoneLabs\vsmon.exe
C:\WINDOWS\System32\MsPMSPSv.exe
C:\WINDOWS\Explorer.EXE
C:\WINDOWS\system32\taskmgr.exe
C:\Programmi\Zone Labs\ZoneAlarm\zlclient.exe
C:\Programmi\Nokia\Nokia PC Suite 6\LaunchApplication.exe
C:\PROGRA~1\FILECO~1\PCSuite\Services\SERVIC~1.EXE
C:\Programmi\Nokia\Nokia PC Suite 6\OneTouchAccess.exe
C:\Programmi\Mozilla Firefox\firefox.exe
C:\Documents and Settings\idril\Documenti\Programmi\HijackThis\HijackThis.exe

R0 - HKCU\Software\Microsoft\Internet Explorer\Main,Start Page = http://www.google.it/
R0 - HKCU\Software\Microsoft\Internet Explorer\Toolbar,LinksFolderName = Collegamenti
O2 - BHO: AcroIEHlprObj Class - {06849E9F-C8D7-4D59-B87D-784B7D6BE0B3} - C:\Programmi\Adobe\Acrobat 7.0\ActiveX\AcroIEHelper.dll
O2 - BHO: (no name) - {53707962-6F74-2D53-2644-206D7942484F} - C:\PROGRA~1\SPYBOT~1\SDHelper.dll
O2 - BHO: Google Toolbar Helper - {AA58ED58-01DD-4d91-8333-CF10577473F7} - c:\programmi\google\googletoolbar1.dll
O2 - BHO: AcroIEToolbarHelper Class - {AE7CD045-E861-484f-8273-0445EE161910} - C:\Programmi\Adobe\Acrobat 7.0\Acrobat\AcroIEFavClient.dll
O3 - Toolbar: &Google - {2318C2B1-4965-11d4-9B18-009027A5CD4F} - c:\programmi\google\googletoolbar1.dll
O3 - Toolbar: Adobe PDF - {47833539-D0C5-4125-9FA8-0819E2EAAC93} - C:\Programmi\Adobe\Acrobat 7.0\Acrobat\AcroIEFavClient.dll
O8 - Extra context menu item: Convert link target to Adobe PDF - res://C:\Programmi\Adobe\Acrobat 7.0\Acrobat\AcroIEFavClient.dll/AcroIECapture.html
O8 - Extra context menu item: Convert link target to existing PDF - res://C:\Programmi\Adobe\Acrobat 7.0\Acrobat\AcroIEFavClient.dll/AcroIEAppend.html
O8 - Extra context menu item: Convert selected links to Adobe PDF - res://C:\Programmi\Adobe\Acrobat 7.0\Acrobat\AcroIEFavClient.dll/AcroIECaptureSelLinks.html
O8 - Extra context menu item: Convert selected links to existing PDF - res://C:\Programmi\Adobe\Acrobat 7.0\Acrobat\AcroIEFavClient.dll/AcroIEAppendSelLinks.html
O8 - Extra context menu item: Convert selection to Adobe PDF - res://C:\Programmi\Adobe\Acrobat 7.0\Acrobat\AcroIEFavClient.dll/AcroIECapture.html
O8 - Extra context menu item: Convert selection to existing PDF - res://C:\Programmi\Adobe\Acrobat 7.0\Acrobat\AcroIEFavClient.dll/AcroIEAppend.html
O8 - Extra context menu item: Convert to Adobe PDF - res://C:\Programmi\Adobe\Acrobat 7.0\Acrobat\AcroIEFavClient.dll/AcroIECapture.html
O8 - Extra context menu item: Convert to existing PDF - res://C:\Programmi\Adobe\Acrobat 7.0\Acrobat\AcroIEFavClient.dll/AcroIEAppend.html
O8 - Extra context menu item: E&sporta in Microsoft Excel - res://C:\PROGRA~1\MICROS~2\OFFICE11\EXCEL.EXE/3000
O9 - Extra button: (no name) - {08B0E5C0-4FCB-11CF-AAA5-00401C608501} - C:\Programmi\Java\jre1.5.0_01\bin\npjpi150_01.dll
O9 - Extra 'Tools' menuitem: Sun Java Console - {08B0E5C0-4FCB-11CF-AAA5-00401C608501} - C:\Programmi\Java\jre1.5.0_01\bin\npjpi150_01.dll
O9 - Extra button: Ricerche - {92780B25-18CC-41C8-B9BE-3C9C571A8263} - C:\PROGRA~1\MICROS~2\OFFICE11\REFIEBAR.DLL
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
O16 - DPF: {2BC66F54-93A8-11D3-BEB6-00105AA9B6AE} (Symantec AntiVirus scanner) - http://security.symantec.com/sscv6/SharedContent/vc/bin/AvSniff.cab
O16 - DPF: {6414512B-B978-451D-A0D8-FCFDF33E833C} (WUWebControl Class) - http://update.microsoft.com/windowsupdate/v6/V5Controls/en/x86/client/wuweb_site.cab?1156893728078
O16 - DPF: {644E432F-49D3-41A1-8DD5-E099162EEEC5} (Symantec RuFSI Utility Class) - http://security.symantec.com/sscv6/SharedContent/common/bin/cabsa.cab
O17 - HKLM\System\CCS\Services\Tcpip\..\{A5281875-85A7-4959-9FA6-BB3EFA837BFA}: NameServer = 213.230.130.222 213.230.155.94
O18 - Protocol: livecall - {828030A1-22C1-4009-854F-8E305202313F} - C:\PROGRA~1\MSNMES~1\MSGRAP~1.DLL
O18 - Protocol: msnim - {828030A1-22C1-4009-854F-8E305202313F} - C:\PROGRA~1\MSNMES~1\MSGRAP~1.DLL
O20 - Winlogon Notify: WgaLogon - C:\WINDOWS\SYSTEM32\WgaLogon.dll
O23 - Service: Adobe LM Service - Adobe Systems - C:\Programmi\File comuni\Adobe Systems Shared\Service\Adobelmsvc.exe
O23 - Service: AVG7 Alert Manager Server (Avg7Alrt) - GRISOFT, s.r.o. - C:\PROGRA~1\Grisoft\AVGFRE~1\avgamsvr.exe
O23 - Service: AVG7 Update Service (Avg7UpdSvc) - GRISOFT, s.r.o. - C:\PROGRA~1\Grisoft\AVGFRE~1\avgupsvc.exe
O23 - Service: AVG E-mail Scanner (AVGEMS) - GRISOFT, s.r.o. - C:\PROGRA~1\Grisoft\AVGFRE~1\avgemc.exe
O23 - Service: Creative Service for CDROM Access - Creative Technology Ltd - C:\WINDOWS\System32\CTSvcCDA.EXE
O23 - Service: Sandra Data Service (SandraDataSrv) - SiSoftware - C:\Programmi\SiSoftware\SiSoftware Sandra Lite 2007.SP1\Win32\RpcDataSrv.exe
O23 - Service: Sandra Service (SandraTheSrv) - SiSoftware - C:\Programmi\SiSoftware\SiSoftware Sandra Lite 2007.SP1\RpcSandraSrv.exe
O23 - Service: TrueVector Internet Monitor (vsmon) - Zone Labs, LLC - C:\WINDOWS\system32\ZoneLabs\vsmon.exe

Grazie per la pazienza!

Fatto anche questo, ma il problema persiste. Qualche altro consiglio?
Grazie, ancora.