Homeland Security: Illegal immigration into the U.S. puts our homeland security at risk and opens doors to possible terrorism

The subject is Homeland Security, it just wasn't listed in the drop down. In addition to how illegal immigration puts our homeland security at risk, I would like the paper to mention the risk caused by legal immigration as well. Like, improper screening and tracking of visa applicants, that sort of thing. However the main focus is on the risk caused by illegal immigration. Also, a couple of reasonable and feasible solutions to better border controls to reduce illegal immigration into the U.S..