Explorer.exe repeatedly restarting!

[Militant Agnostic]

Windows explorer is repeatedly restarting, I think because of a Trojan or a badly written virus. The taskbar and icons are disappearing and reappearing at a regular rate, making the computer pretty much unusable. I did a spyware scan and found and deleted a trojan dropper but the problem persists.

Here's my HijackThis Log:

Logfile of Trend Micro HijackThis v2.0.2
Scan saved at 8:14:05 AM, on 6/8/2008
Platform: Windows XP SP2 (WinNT 5.01.2600)
MSIE: Internet Explorer v7.00 (7.00.6000.16640)
Boot mode: Normal

Running processes:
C:\WINDOWS\System32\smss.exe
C:\WINDOWS\system32\csrss.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:\Program Files\PC Tools Firewall Plus\FWService.exe
C:\WINDOWS\system32\svchost.exe
C:\WINDOWS\System32\svchost.exe
C:\WINDOWS\system32\svchost.exe
C:\WINDOWS\system32\Ati2evxx.exe
C:\WINDOWS\system32\svchost.exe
C:\WINDOWS\system32\svchost.exe
C:\Program Files\Alwil Software\Avast4\aswUpdSv.exe
C:\Program Files\Alwil Software\Avast4\ashServ.exe
C:\Program Files\Alwil Software\Avast4\ashMaiSv.exe
C:\WINDOWS\system32\LEXBCES.EXE
C:\WINDOWS\system32\spoolsv.exe
C:\WINDOWS\system32\LEXPPS.EXE
C:\Program Files\a-squared Anti-Malware\a2service.exe
C:\WINDOWS\system32\PnkBstrA.exe
C:\Program Files\Sunbelt Software\CounterSpy\SBCSSvc.exe
C:\Program Files\Spyware Doctor\pctsAuxs.exe
C:\Program Files\Spyware Doctor\pctsSvc.exe
C:\Program Files\Spyware Doctor\pctsTray.exe
C:\WINDOWS\system32\svchost.exe
C:\Program Files\ThreatFire\TFService.exe
c:\WINDOWS\system32\ZuneBusEnum.exe
C:\WINDOWS\system32\WgaTray.exe
C:\WINDOWS\System32\alg.exe
C:\Program Files\Mozilla Firefox\firefox.exe
C:\Program Files\Trend Micro\HijackThis\HijackThis.exe
C:\WINDOWS\system32\wbem\wmiprvse.exe
C:\WINDOWS\explorer.exe
C:\WINDOWS\system32\imapi.exe

R3 - URLSearchHook: Yahoo! Toolbar - {EF99BD32-C1FB-11D2-892F-0090271D4F88} - C:\Program Files\Yahoo!\Companion\Installs\cpn\yt.dll
O3 - Toolbar: Yahoo! Toolbar - {EF99BD32-C1FB-11D2-892F-0090271D4F88} - C:\Program Files\Yahoo!\Companion\Installs\cpn\yt.dll
O4 - HKLM\..\Run: [Windows Defender] "C:\Program Files\Windows Defender\MSASCui.exe" -hide
O4 - HKLM\..\Run: [SoundMan] SOUNDMAN.EXE
O4 - HKLM\..\Run: [RemoteControl] "C:\Program Files\CyberLink\PowerDVD\PDVDServ.exe"
O4 - HKLM\..\Run: [NeroFilterCheck] C:\Program Files\Common Files\Ahead\Lib\NeroCheck.exe
O4 - HKLM\..\Run: [ISTray] "C:\Program Files\Spyware Doctor\pctsTray.exe"
O4 - HKCU\..\Run: [AWMON] "E:\Program Files\Lavasoft\Ad-Aware SE Plus\Ad-Watch.exe"
O4 - HKUS\S-1-5-18\..\Run: [Picasa Media Detector] C:\Program Files\Picasa2\PicasaMediaDetector.exe (User 'SYSTEM')
O4 - HKUS\.DEFAULT\..\Run: [Picasa Media Detector] C:\Program Files\Picasa2\PicasaMediaDetector.exe (User 'Default user')
O4 - Startup: MagicDisc.lnk = C:\Program Files\MagicDisc\MagicDisc.exe
O4 - Startup: OneNote 2007 Screen Clipper and Launcher.lnk = C:\Program Files\Microsoft Office\Office12\ONENOTEM.EXE
O8 - Extra context menu item: E&xport to Microsoft Excel - res://C:\PROGRA~1\MICROS~2\Office10\EXCEL.EXE/3000
O9 - Extra button: (no name) - {08B0E5C0-4FCB-11CF-AAA5-00401C608501} - C:\Program Files\Java\jre1.6.0_01\bin\ssv.dll
O9 - Extra 'Tools' menuitem: Sun Java Console - {08B0E5C0-4FCB-11CF-AAA5-00401C608501} - C:\Program Files\Java\jre1.6.0_01\bin\ssv.dll
O9 - Extra button: Send to OneNote - {2670000A-7350-4f3c-8081-5663EE0C6C49} - C:\PROGRA~1\MICROS~2\Office12\ONBttnIE.dll
O9 - Extra 'Tools' menuitem: S&end to OneNote - {2670000A-7350-4f3c-8081-5663EE0C6C49} - C:\PROGRA~1\MICROS~2\Office12\ONBttnIE.dll
O9 - Extra button: Research - {92780B25-18CC-41C8-B9BE-3C9C571A8263} - C:\PROGRA~1\MICROS~2\Office12\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:\Program Files\Messenger\msmsgs.exe
O9 - Extra 'Tools' menuitem: Windows Messenger - {FB5F1910-F110-11d2-BB9E-00C04F795683} - C:\Program Files\Messenger\msmsgs.exe
O16 - DPF: {30528230-99f7-4bb4-88d8-fa1d4f56a2ab} (YInstStarter Class) - C:\Program Files\Yahoo!\Common\yinsthelper.dll
O16 - DPF: {8167C273-DF59-4416-B647-C8BB2C7EE83E} (WebSDev Control) - http://liveupdate.msi.com.tw/autobio...ne/install.cab
O18 - Protocol: grooveLocalGWS - {88FED34C-F0CA-4636-A375-3CB6248B04CD} - C:\PROGRA~1\MICROS~2\Office12\GR99D3~1.DLL
O18 - Protocol: skype4com - {FFC8B962-9B40-4DFF-9458-1830C7DD7F5D} - C:\PROGRA~1\COMMON~1\Skype\SKYPE4~1.DLL
O23 - Service: a-squared Anti-Malware Service (a2AntiMalware) - Emsi Software GmbH - C:\Program Files\a-squared Anti-Malware\a2service.exe
O23 - Service: Adobe LM Service - Adobe Systems - C:\Program Files\Common Files\Adobe Systems Shared\Service\Adobelmsvc.exe
O23 - Service: Apple Mobile Device - Apple, Inc. - C:\Program Files\Common Files\Apple\Mobile Device Support\bin\AppleMobileDeviceService.exe
O23 - Service: avast! iAVS4 Control Service (aswUpdSv) - ALWIL Software - C:\Program Files\Alwil Software\Avast4\aswUpdSv.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: avast! Antivirus - ALWIL Software - C:\Program Files\Alwil Software\Avast4\ashServ.exe
O23 - Service: avast! Mail Scanner - ALWIL Software - C:\Program Files\Alwil Software\Avast4\ashMaiSv.exe
O23 - Service: avast! Web Scanner - ALWIL Software - C:\Program Files\Alwil Software\Avast4\ashWebSv.exe
O23 - Service: Bonjour Service - Apple Inc. - C:\Program Files\Bonjour\mDNSResponder.exe
O23 - Service: FLEXnet Licensing Service - Macrovision Europe Ltd. - C:\Program Files\Common Files\Macrovision Shared\FLEXnet Publisher\FNPLicensingService.exe
O23 - Service: Google Updater Service (gusvc) - Google - C:\Program Files\Google\Common\Google Updater\GoogleUpdaterService.exe
O23 - Service: InstallDriver Table Manager (IDriverT) - Macrovision Corporation - C:\Program Files\Common Files\InstallShield\Driver\11\Intel 32\IDriverT.exe
O23 - Service: iPod Service - Apple Inc. - C:\Program Files\iPod\bin\iPodService.exe
O23 - Service: LexBce Server (LexBceS) - Lexmark International, Inc. - C:\WINDOWS\system32\LEXBCES.EXE
O23 - Service: NVIDIA Display Driver Service (NVSvc) - NVIDIA Corporation - C:\WINDOWS\system32\nvsvc32.exe
O23 - Service: PC Tools Firewall Plus (PCToolsFirewallPlus) - PC Tools - C:\Program Files\PC Tools Firewall Plus\FWService.exe
O23 - Service: PnkBstrA - Unknown owner - C:\WINDOWS\system32\PnkBstrA.exe
O23 - Service: Sunbelt CounterSpy Antispyware (SBCSSvc) - Sunbelt Software - C:\Program Files\Sunbelt Software\CounterSpy\SBCSSvc.exe
O23 - Service: PC Tools Auxiliary Service (sdAuxService) - PC Tools - C:\Program Files\Spyware Doctor\pctsAuxs.exe
O23 - Service: PC Tools Security Service (sdCoreService) - PC Tools - C:\Program Files\Spyware Doctor\pctsSvc.exe
O23 - Service: ThreatFire - PC Tools - C:\Program Files\ThreatFire\TFService.exe

--
End of file - 7023 bytes

[Lisandro]

I did a spyware scan and found and deleted a trojan dropper

Can you say what is the infected file name, where was it found (C:\windows\system32\infected-file-name.xxx)?

I suggest:

1. Disable System Restore and reenable it after step 3.
2. Clean your temporary files.
3. Schedule a boot time scanning with avast with archive scanning turned on.
4. Use SUPERantispyware, MBAM or Spyware Terminator to scan for spywares and trojans. If any infection is detected, better and safer is send the file to Quarantine than to simple delete than.
5. Test your machine with anti-rootkit applications. I suggest avast! antirootkit or Trend Micro RootkitBuster.

[Militant Agnostic]

I did a bootime scan with avast antivirus. Also scanned for rootkits and spyware with ThreatFire and Spyware Doctor. Ran CCleaner to delete temporary files.

The problem persists but less frequently. Maybe every fifteen minutes now instead of thirty seconds.

The Trojan Dropper I found was automatically deleted by my scanner because I set it to do that. So I don't know here it was.