Buenas,me ha pasado exactamente el mismo problema.
He seguido los pasos que indica iroc9555 (ejecutar adwcleaner y malwarebytes) y hasta el momento parece que el problema ha desparecido.
Pego aquí los informes de ambos para saber si debería preocuparme por algo.
Gracias y un saludo.
Malwarebytes Anti-Malware
www.malwarebytes.org
Scan Date: 17/01/2015
Scan Time: 13:54:41
Logfile: bytes.txt
Administrator: Yes
Version: 2.00.4.1028
Malware Database: v2015.01.17.02
Rootkit Database: v2015.01.14.01
License: Trial
Malware Protection: Enabled
Malicious Website Protection: Enabled
Self-protection: Disabled
OS: Windows 7 Service Pack 1
CPU: x64
File System: NTFS
User: Martín
Scan Type: Threat Scan
Result: Completed
Objects Scanned: 351034
Time Elapsed: 21 min, 36 sec
Memory: Enabled
Startup: Enabled
Filesystem: Enabled
Archives: Enabled
Rootkits: Disabled
Heuristics: Enabled
PUP: Enabled
PUM: Enabled
Processes: 0
(No malicious items detected)
Modules: 0
(No malicious items detected)
Registry Keys: 2
PUP.Optional.Babylon.A, HKU\S-1-5-18-{ED1FC765-E35E-4C3D-BF15-2C2B11260CE4}-0\SOFTWARE\MICROSOFT\INTERNET EXPLORER\SEARCHSCOPES{0ECDF796-C2DC-4d79-A620-CCE0C0A66CC9}, Quarantined, [1066e315e9a09a9c0f60717a51b1d729],
PUP.Optional.PlusHD.A, HKU\S-1-5-18-{ED1FC765-E35E-4C3D-BF15-2C2B11260CE4}-0\SOFTWARE\APPDATALOW\SOFTWARE\Plus-HD-7.5, Quarantined, [caacad4b147591a5651dc6e39f643bc5],
Registry Values: 0
(No malicious items detected)
Registry Data: 0
(No malicious items detected)
Folders: 0
(No malicious items detected)
Files: 1
PUP.Optional.Conduit.A, C:\Users\Martín\AppData\Local\CRE\ejpbbhjlbipncjklfjjaedaieimbmdda.crx, Quarantined, [5e180cec4e3b80b614009af49b6834cc],
Physical Sectors: 0
(No malicious items detected)
(end)