Broken Boarders

Many have postulated that --seeing as how illegal immigrants can so easily hop across the Mexican-American boarder-- a determined terrorist could just as easily do the same thing. They thus conclude that boarder security is of the utmost importance for national security. If you go here, it looks as though something very close to this theoretical situation has just happened. True, we don't know for sure that these Syrians are terrorists, but there's a good enough chance that we should be alarmed. And even if they're not terrorist, how long will it be till terrorist catch on to one of America's biggest vulnerabilities?