I’m running Avast 8:free version 130404-0. My Internet Explorer default web page is “about:blank”. When I opened up Internet Explorer I go a warning message from Avast saying “This site has been marked as a phishing site”. I had 3 options for a response:
“Get Me Out of This”, “Trust This Domain”, Ignore the Warning" . Is this a problem with Avast, or should I be concerned about the web site “about:blank” ?
Here is a link that may or may not help http://en.wikipedia.org/wiki/About:blank#Common_about:_URIs
about:blank is “not” a website per se. 
Strange I don’t get any alert for about:blank in IE8, nor do I get it on my win7 netbook with IE10. Not sure what your settings might be in regard to phishing - AvastUI > Settings > WebRep & Antiphishing.
I think I know why, in my IE versions I don’t have the webrep enabled and the anti-phishing is tied to that. In XP I have the latest beta of avast and have disabled the webrep in firefox 20.0 as it messes with the layout.
That leaves firefox 20.0 in the win7 netbook with the 8.0.1483 version of avast. When I type about:blank and enter, that is changed to about:newtab, but I don’t get any anti-phishing alert.
Given that this is a pretty common non-internet address I don’t really know why it might be considered a phishing address.
It’s my understanding that you do “not” need WebRep enabled for anti-phishing to work.
They are not interdependent upon each other. According to the built-in help file.
Well as far as I’m aware the phishing notice page is compiled by the same function, but I could be wrong, it could be done by the web shield.
Though if it were done by the web shield it would mean that my previous statement is somewhat invalidated as it doesn’t require the webrep. So it should also have alerted on my XP system with the avast beta version without the webrep.
What would really help is if the OP could provide a screenshot of the pop-up message. ???