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Combatting Web Bots: Strategies against Malicious Programs Online

Learn how to distinguish humans from web bots, create effective CAPTCHAs, and understand OCR technology to combat spam and protect online accounts.

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Combatting Web Bots: Strategies against Malicious Programs Online

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  1. Fighting the WebBots • A webbot is a program that visits web sites for all kinds of purposes. • For example, Google webbots make copies of all web sites for their search engines. • The challenge is to stop malicious webbots ITS102-12, Third Class

  2. Webbots and Spam • Spammers send webbots to get e-mail accounts from sites that offer them for free. • How can you tell that someone who asks for an e-mail account is a person or a webbot? ITS102-12, Third Class

  3. Are you a person or a bot? • We know that there are certain things that computers cannot do. • Ask the “applicant” to do something that computers cannot do. • Cook a meal? • Read something impossible for computers to read! ITS102-12, Third Class

  4. CAPTCHA • CompletelyAutomatedPublicTuring test to tellComputers andHumansApart ITS102-12, Third Class

  5. CAPTCHA • CAPTCHA does not have to be text, but “computer unreadable” text is convenient. • Alternatives include pictures. • For example, ask if a person in a pictures is smiling or not. What is wrong with such a CAPTCHA ITS102-12, Third Class

  6. How Computers ReadOptical Character Recognition (OCR) • Step 1: Separate print (usually dark) from background (usually light). • Step 2: Pick up individual characters (group of dark pixels) • Step 3: Identify their shape by looking for strokes, loops, corners, etc • Step 4: Use rules to classify. For example, an H has two vertical strokes and a short horizontal strokes. ITS102-12, Third Class

  7. Frustrating OCR ITS102-12, Third Class

  8. Make your own CAPTCHA • A web site that offers you the means: • www.codeproject.com/KB/aspnet/CaptchaImage.aspx • For a general tutorial see: • www.theopavlidis.com/technology/captcha/tutorial.htm ITS102-12, Third Class

  9. Some Weak CAPTCHAs From Paypal From Yahoo’sBriefcase ITS102-12, Third Class

  10. Some CAPTCHAs that may betoo hard for people From Yahoo: From Passport: ITS102-12, Third Class

  11. But Human Vision is Amazing ITS102-12, Third Class

  12. But Human Vision is Amazing ITS102-12, Third Class

  13. Non Text CAPTCHAs • Use pictures as CAPTCHAs • Plus: There are very tough to break • Minus: • Need to label a huge number of pictures. • If we use few pictures the webbot can just keep guessing. ITS102-12, Third Class

  14. Synthetic Pictures(an idea by M. Kaplan) Please click on or enter each letter corresponding to the following list in the field below. You must enter them in the exact sequence listed. C K ITS102-12, Third Class

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