If you're read the site, you probably know that Furbies aren't as smart as everyone thinks they are. The toymakers created the illusion that it learned English because it's vocabulary became more and more robust as time went on. However, most people thought (and think) that Furbies actually learn English and that they repeat stuff that they hear.
Because of this, several intelligence agencies banned Furbies from their offices because they were afraid that they were going to hear classified information and repeat it at a later time. Surely Furbies were planning a world-takeover and these measures prevented a disaster.