Hello.
You have not provided much information to go on but one possibility i can think of is that the brower home page and any page you search for is hijacked and trying to redirect you to malicious web pages. Thus you receiving the message about the address being blocked.
Could you check what your homepage is currently set to? The option to view/change should be within Internet explorer under 'Internet Options'
Also please be more descriptive on the actual message, is it an AntiVirus message or a firewall message?
You could also use a program called 'Hijackthis' from TrendMicro. It checks registry and files settings, it can also be used to spot files/settings that should not be there or are causing issues.
http://uk.trendmicro.com/uk/products/personal/free-tools-and-services/You can if you wish post the log file you save from the scan here so that it can be viewed one of us may find something there that is the cause. - Do not 'fix' anything within 'hijackthis' yet.
Also other programs such as Malwarebytes Anti-Malware are a help. - Worth doing a scan with that too, you may find many more unwanted items lying around.
Plus even if the cause is nothing malicious it is better to be safe then sorry.