There are many ways for someone to hijack your browser.......
The hijacker could be a .dll file or an .exe file or a .reg file or a combination of any of these. It could be in the root C:\ directory or C:\Windows or C:\Windows\system or just about any other directory. There is no constant, everything is variable, the only certain thing is that it is getting through a security loophole on your computer, be it security settings or a lack of patches/updates.
(1)
First thing to do....click tools...Windows update..... and download all critical updates.
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Second is to download and install Spywareblaster.
(3)
Third download and install Spywareguard.
These programs take up very little resources and run un-noticed in the background.
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Fourth download and install Spybot Search and Destroy.
Always check for updates before running. Click the immunize button..... and while you're there (at this page) you can lock your homepage if you want to. As with an anti-virus program - check for updates at least once a week, with all the above programs.
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Fifth download IE-SPYAD.
Installation instructions here :-
IE-SPYAD
stops advertisers and marketers from automatically installing adware
onto your PC without your permission.
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Install this HOSTS file onto your computer -- it will block your PC from accessing known malicious web sites, sites that contain viruses and malware.
None of this can guarantee 100% that you won't be hijacked - but it will certainly go a long way.
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Make sure you have a firewall. (More info)