Programmers don't seem to understand what makes a CAPTCHA difficult to "break". But it's not difficult to find out. Heck, the hackers themselves will tell you how to do CAPTCHA correctly if you just know where to look. For example, this Chinese hacker's page breaks down a number of common CAPTCHAs , and the price of software he sells to defeat them at a certain percentage success rate:
| the9 100% $500 |  |
| dvbbs 95% $1,000 |  |
| Shanda 90% $1,500 |  |
| Baidu 80% $3,000 |  |
| eBay 70% $4,000 |  |
| Ticketmaster 50% $6,000 |  |
| Google (unbreakable) |  |
| Hotmail (unbreakable) |  |
| Yahoo (unbreakable) |  |