CAPTCHAs are simply distorted images of encoded text that are displayed
alongside a text box that the user is challenged to enter the encoded text into. Once
again, this is done to ensure that a human being is at the other end of the terminal using
the web application and not some automated program. Although the CAPTCHA controls
can offer somewhat better security, they also have the downside of causing extra inconvenience
for the users. Not only do they require additional input from the user, but they
could be at times cumbersome to read. They are also not 100% bullet proof as more
advanced crawlers use OCR technology to decipher the encoded text in them.
NoBot attempts to provide the same functionality as CAPTCHA controls without
requiring the user to read and enter cryptic text. It??™s essentially invisible and works by setting
a number of parameters designed to protect against the bots. One such measure is to
request the browser to perform a simple JavaScript task, which can help ensure there is a
browser at the other end. Figure 8-8 shows a sample page with login information using
the NoBot extender without asking the user for any additional information.
Pages:
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262