What: Shares of home and business security specialist ADT Corp. (NYSE: ADT) were off 11.8% at 11:50 a.m. ET on Tuesday after its quarterly results disappointed Wall Street.

So what: ADT shares have slumped over the past year on concerns over intensifying competition, and today's top-line miss -- Q1 revenue of $900 million versus the consensus of $906 million -- suggests that its growth trajectory is indeed being slowed down. So while the company's adjusted EPS of $0.49 managed to top estimates, the revenue increase of less than 1% coupled with a decline of 30 basis points in EBITDA margin reinforces serious worries over its competitive position going forward. 

Now what: Management remains confident that it will be able to capitalize on long-term growth opportunities, particularly the $24 billion market opportunity in business and health. "Our quality growth plan is improving our financial performance and will position us for lower attrition and higher levels of free cash flow" said CEO Naren Gursahaney. "We're also investing in our traditional business and expanding into adjacencies, creating more growth opportunities in the future." Given ADT's massive debt load and worrisome top-line trend, however, I wouldn't bet too heavily on that bullishness.