Just now try to install CCleaner. Installation stop 50%. I don't know may be your update server fall down, may be my network or dns problem. I close network and install it successfully.
CCleaner shouldn't be using your network while installing.
CCleaner calls home while installing to check what version you are installing.
My firewall always asks me when I am installing a new ccleaner version if I want to allow it to call home, I say no
It doesn't stop it installing, just doesn't let it call home on install.
PROTIP: once you've installed ccleaner once you can unzip the portable version into your ccleaner folder, this avoids the call home and google offer and can still uninstall and use non portable settings, don't extract portable.dat though or it'll lock those settings and move you to an ini file in the ccleaner folder
This look like usual problem of applications which use IE wininet.dll libraries for Internet connections in synchronous mode. decision is asynchronous mode or wsock32.dll. which more complicate but correct