Access to Non-productive Web Sites
Although not a glaring security risk, but by denying access to specific sites, employees will not be tempted to do such things as on-line gambling, checking personal emails, etc.
On the security
front, some of the sites do require a program, such as a shareware be downloaded,
which is a potential "hole" into your network. Another item to consider
is that a lot of the casino, on-lining trading and the ever popular adult content
sites, have those annoying popups, which have been known to launch malware,
viruses, shareware, self extracting executables, etc, which is a security breach.