It's there a source for this? I find it hard to believe that some idiot hadn't tried to bring something onboard in the past 15 years.
[1] http://www.nbcnews.com/news/us-news/investigation-breaches-u...
Slate has another article from 2010 you might enjoy http://www.slate.com/articles/news_and_politics/explainer/20...
Security guards don't go trumpeting how many bank robberies they've thwarted, because they simply don't know.
However, they will tell you about all the contraband they've confiscated simply because that's measurable.
Their justification is that they stop hundreds of bits of contraband (of which they control the definition) daily in the ongoing war on terror.
They failed to detect the other 67 who were able to embark planes with weapons end explosives[0]. But that's just a detail... You know, these agents were instructed to avoid TSA screening. Who trains to do that in the real world, right? [sarcasm]
[0] http://abcnews.go.com/US/exclusive-undercover-dhs-tests-find...