Scan your system for pests like spyware and adware.
Another option for you to protect yourself from virtual pests.

Search and destroy spyware, adware, hijackers and other malware.
Bazooka detects and removes numerous spyware, adware, keyloggers, etc.
Tool that diagnoses and removes DLLs infected with viruses and other pests.
BioScanner allows you to identify helper objects that are installed in your browser.