WinFixer pop-ups are caused by a hidden adware program installed on the affected PC. WinFixer adware can install itself without your knowledge and permission when visiting certain websites, or it may be packaged with freeware. It displays deceptive pop-up ads that have the appearance of system alert messages which are unassociated with any software, and prompts you to purchase WinFixer 2005 to fix a reported system problem.

To remove WinFixer and its pop-ups it's worthwhile starting with your Control Panel Add/Remove Programs utility as some variants may be removed from there. Look for WinFixer in the list of installed programs and follow the prompts to remove it. Then scan your system with an advanced anti-adware program such as XoftSpySE to make sure it's completely removed from your system and incapable of re-installing itself. If all its components are not completely removed it may automatically re-install itself at some later time or the next time your reboot your system.

To prevent future infections by WinFixer or other adware programs be aware that freeware programs often bundle adware programs with them. Always read the terms and conditions to find out exactly what software you're loading onto your machine. To block drive-by-downloads when visiting bad websites, make sure you have the latest Windows patches, use an up-to-date anti-adware program such as XoftSpySE that has real time protection and configure your system so that programs cannot install without your knowledge or permission:

1. Go to Tools → Internet Options and select Advanced. Uncheck 'Enable Install On Demand' and 'Allow Software To Run or Install'.

2. Go to Security tab → Internet → Custom level. Set 'Download Unsigned Controls' and 'Initialize and Script ActiveX controls not marked as safe' to Disable. Set 'Download Signed Controls' to Prompt.

Source: remove-winfixer.com