Passwords with fewer than 12 characters can be quickly brute-force decoded using a PC graphics processing unit (GPU) that costs just a few hundred dollars, according to researchers at the Georgia Institute of Technology.

"We've been using a commonly available graphics processor to test the integrity of typical passwords of the kind in use here at Georgia Tech and many other places," said Richard Boyd, a senior research scientist at the university's research institute, in a statement. "Right now we can confidently say that a seven-character password is hopelessly inadequate."

Today's top graphics processors offer about two teraflops of parallel processing power. For comparison, "in the year 2000, the world's fastest supercomputer, a cluster of linked machines costing $110 million, operated at slightly more than 7 teraflops," he said.

The barrier to using multi-core graphics processors -- available from Nvidia or AMD's ATI division -- for compute-intensive processes other than graphics processing, said Boyd, first fell in 2007, when Nvidia released a C-based software development kit. "Once Nvidia did that, interest in GPUs really started taking off," he said. "If you can write a C program, you can program a GPU now." Or use it to crack a password.

Furthermore, thanks to Moore's Law, graphics processors continue to increase in power, which means that GPUs will get better, not worse, at cracking passwords.

But who needs a graphics processor? People often create and rely on simple passwords, and many websites use passwords more for psychological than security purposes.

But the Georgia Tech research underscores the importance of getting people to adopt longer, non-simple passwords to make them safer against attack. "Length is a major factor in protecting against 'brute forcing' a password," according to one research scientist involved in the project, Joshua Davis. "A computer keyboard contains 95 characters, and every time you add another character, your protection goes up exponentially, by 95 times."

For the record, to defend against GPU attacks, the password researchers recommend using sentence-length passwords that mix letters with numbers or symbols, and which are at least 12 characters long.