Web Mail May Conflict With Adware
Adware, software that replaces advertisements with its own, may interfere with Web Mail. To check your Windows system for adware, you can download a free utility such as Ad-aware from Lavasoft.
Spybot Search & Destroy by PepiMK Software also scans for spyware, software that allows a stranger to remotely monitor and control your computer.
Mac OS users can download SecureMac.com's MacScan although the Mac OS is generally not targeted by adware or spyware.