Ciao cbbusto, grazie per la risposta.
Ecco il log di Hijackthis:
Logfile of Trend Micro HijackThis v2.0.4
Scan saved at 3:19:37 , on 05/09/2012
Platform: Windows XP SP3 (WinNT 5.01.2600)
MSIE: Internet Explorer v6.00 SP3 (6.00.2900.5512)
Boot mode: Normal
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:\Programmi\Sandboxie\SbieSvc.exe
C:\WINDOWS\System32\svchost.exe
C:\WINDOWS\system32\Ati2evxx.exe
C:\WINDOWS\system32\spoolsv.exe
C:\Programmi\Avira\AntiVir Desktop\sched.exe
C:\WINDOWS\Explorer.EXE
C:\Programmi\Avira\AntiVir Desktop\avgnt.exe
C:\Programmi\Avira\AntiVir Desktop\avfwsvc.exe
C:\Programmi\Avira\AntiVir Desktop\avguard.exe
C:\Programmi\Secunia\PSI\PSIA.exe
C:\WINDOWS\system32\svchost.exe
C:\Programmi\Avira\AntiVir Desktop\avshadow.exe
C:\Programmi\Avira\AntiVir Desktop\avmailc.exe
C:\Programmi\Avira\AntiVir Desktop\AVWEBGRD.EXE
C:\WINDOWS\system32\dllhost.exe
C:\Programmi\HitmanPro\hmpsched.exe
C:\Programmi\Sandboxie\SbieCtrl.exe
C:\WINDOWS\system32\msiexec.exe
C:\Programmi\Trend Micro\HiJackThis\HiJackThis.exe
R1 - HKCU\Software\Microsoft\Windows\CurrentVersion\Internet Settings,ProxyOverride = 127.0.0.1
R0 - HKCU\Software\Microsoft\Internet Explorer\Toolbar,LinksFolderName = Collegamenti
O4 - HKLM\..\Run: [avgnt] "C:\Programmi\Avira\AntiVir Desktop\avgnt.exe" /min
O4 - HKUS\S-1-5-19\..\Run: [CTFMON.EXE] C:\WINDOWS\system32\CTFMON.EXE (User 'SERVIZIO LOCALE')
O4 - HKUS\S-1-5-20\..\Run: [CTFMON.EXE] C:\WINDOWS\system32\CTFMON.EXE (User 'SERVIZIO DI RETE')
O4 - HKUS\S-1-5-18\..\Run: [CTFMON.EXE] C:\WINDOWS\system32\CTFMON.EXE (User 'SYSTEM')
O4 - HKUS\.DEFAULT\..\Run: [CTFMON.EXE] C:\WINDOWS\system32\CTFMON.EXE (User 'Default user')
O8 - Extra context menu item: Add to Google Photos Screensa&ver - res://C:\WINDOWS\system32\GPhotos.scr/200
O8 - Extra context menu item: E&sporta in Microsoft Excel - res://C:\PROGRA~1\MICROS~2\OFFICE11\EXCEL.EXE/3000
O9 - Extra button: Ricerche - {92780B25-18CC-41C8-B9BE-3C9C571A8263} - C:\PROGRA~1\MICROS~2\OFFICE11\REFIEBAR.DLL
O9 - Extra button: (no name) - {e2e2dd38-d088-4134-82b7-f2ba38496583} - C:\WINDOWS\Network Diagnostic\xpnetdiag.exe
O9 - Extra 'Tools' menuitem: @xpsp3res.dll,-20001 - {e2e2dd38-d088-4134-82b7-f2ba38496583} - C:\WINDOWS\Network Diagnostic\xpnetdiag.exe
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: {6414512B-B978-451D-A0D8-FCFDF33E833C} (WUWebControl Class) -
http://update.microsoft.com/windowsupdate/v6/V5Controls/en/x86/client/wuweb_site.cab?1297805855015O16 - DPF: {6E32070A-766D-4EE6-879C-DC1FA91D2FC3} (MUWebControl Class) -
http://www.update.microsoft.com/microsoftupdate/v6/V5Controls/en/x86/client/muweb_site.cab?1297806040250O22 - SharedTaskScheduler: Precaricatore Browseui - {438755C2-A8BA-11D1-B96B-00A0C90312E1} - C:\WINDOWS\system32\browseui.dll
O22 - SharedTaskScheduler: Daemon di cache delle categorie di componenti - {8C7461EF-2B13-11d2-BE35-3078302C2030} - C:\WINDOWS\system32\browseui.dll
O23 - Service: Adobe Flash Player Update Service (AdobeFlashPlayerUpdateSvc) - Adobe Systems Incorporated - C:\WINDOWS\system32\Macromed\Flash\FlashPlayerUpdateService.exe
O23 - Service: Avira FireWall (AntiVirFirewallService) - Avira Operations GmbH & Co. KG - C:\Programmi\Avira\AntiVir Desktop\avfwsvc.exe
O23 - Service: Avira Mail Protection (AntiVirMailService) - Avira Operations GmbH & Co. KG - C:\Programmi\Avira\AntiVir Desktop\avmailc.exe
O23 - Service: Avira Pianificatore (AntiVirSchedulerService) - Avira Operations GmbH & Co. KG - C:\Programmi\Avira\AntiVir Desktop\sched.exe
O23 - Service: Avira Realtime Protection (AntiVirService) - Avira Operations GmbH & Co. KG - C:\Programmi\Avira\AntiVir Desktop\avguard.exe
O23 - Service: Avira Web Protection (AntiVirWebService) - Avira Operations GmbH & Co. KG - C:\Programmi\Avira\AntiVir Desktop\AVWEBGRD.EXE
O23 - Service: Ati HotKey Poller - ATI Technologies Inc. - C:\WINDOWS\system32\Ati2evxx.exe
O23 - Service: ATI Smart - Unknown owner - C:\WINDOWS\system32\ati2sgag.exe
O23 - Service: Google Updater Service (gusvc) - Google - C:\Programmi\Google\Common\Google Updater\GoogleUpdaterService.exe
O23 - Service: HitmanPro Scheduler (HitmanProScheduler) - SurfRight B.V. - C:\Programmi\HitmanPro\hmpsched.exe
O23 - Service: Mozilla Maintenance Service (MozillaMaintenance) - Mozilla Foundation - C:\Programmi\Mozilla Maintenance Service\maintenanceservice.exe
O23 - Service: Sandboxie Service (SbieSvc) - SANDBOXIE L.T.D - C:\Programmi\Sandboxie\SbieSvc.exe
O23 - Service: Secunia PSI Agent - Secunia - C:\Programmi\Secunia\PSI\PSIA.exe
O23 - Service: Secunia Update Agent - Secunia - C:\Programmi\Secunia\PSI\sua.exe
--
End of file - 4989 bytes