It sounds like a potential browser exploit for me. Check your browsers. If you find it in your list of extensions or add-ons, then it is best to remove it now and do a browser cleanup using CCleaner. Next time you should be careful with websites that offer you to download free software because such software may be used to let viruses come in with or without you knowing.
My Computer
Computer type
PC/Desktop
Computer Manufacturer/Model Number
Custom Built
OS
Windows 7 Ultimate x64
CPU
Intel(R) Core(TM) 2 Quad Q8200 @ 2.33 GHz
Motherboard
Asus P5KPL-AM SE Motherboard
Memory
2x2GB Kingston DDR2
Graphics Card(s)
1GB AMD Radeon HD 5450
Sound Card
VIA Technologies High Definition Audio Device
Monitor(s) Displays
Samsung SyncMaster 733NW
Screen Resolution
1440x900
Hard Drives
SEAGATE 320GB Barracuda® 7200.12, SATA 3 Gb/s, 7200 RPM, 16MB cache x 2