hairystuff :
it maybe anti-virus software checking your installers but without specs of your pc its pretty hard to tell why you're getting the hangs.
I ahve Panda Cloud Antivirus (uses low resources).
PC Specs:
i5 2500k @4.5GHz with Cooler Master Hyper 520 N
Asrock Extreme 3 Gen 3 Z68 Motherboard
MSI 7850 OC'ed to Core:1001MHz Memory:1337MHz
G Skill Ripjaws 8gb 1600 MHz (2 x 4gb) Ram
500gb 7200 RPM 16mb cache Seagate Hard Drive
2TB 7200 RPM 64 mb cache Seagate Hard Drive
Haf 922 Case