How many seconds would it take to break your password?

Security breaches of mind-numbing size like those at LinkedIn and EHarmony.com set crypto- and security geeks to chattering about weak passwords and lazy users and the importance of non-alphanumeric characters to security.

And insisting on a particular number of characters in a password is just pointless security-fetish control freakishness, right?

Nope. The number and type of characters make a big difference.

[ Stupid security mistakes: Things you missed while doing the hard stuff ]

How big? Adding a symbol eliminates the possibility of a straight dictionary attack (using, literally, words from a dictionary. Adding a symbol, especially an unusual one, makes it much harder to crack even using rainbow tables (collections of alphanumeric combinations, only some of which include symbols).

How big a difference to length and character make?

Look below and pick which password-cracking jobs you’d want to take on if you were a computer. The examples come from the Interactive Brute Force Password Search Space Calculator: at GRC.com, the love child of from former InfoWorld columnist and freeware contributor Steve Gibson

How long would it take to crack my password: (Includes letters and numbers, no upper- or lower-case and no symbols)

6 characters: 2.25 billion possible combinations

• Cracking online using web app hitting a target site with one thousand guesses per second: 3.7 weeks.
• Cracking offline using high-powered servers or desktops (one hundred billion guesses/second): 0.0224 seconds
• Cracking offline, using massively parallel multiprocessing clusters or grid (one hundred trillion guesses per second: 0.0000224 seconds

10 characters: 3.76 quadrillion possible combinations

• Cracking online using web app hitting a target site with one thousand guesses per second: 3.7 weeks.
• Cracking offline using high-powered servers or desktops (one hundred billion guesses/second): 10.45 hours
• Cracking offline, using massively parallel multiprocessing clusters or grid (one hundred trillion guesses per second: 37.61 seconds.

Add a symbol, make the crack several orders of magnitude more difficult:

6 characters: 7.6 trillion possible combinations

• Cracking online using web app hitting a target site with one thousand guesses per second: 2.4 centuries.
• Cracking offline using high-powered servers or desktops (one hundred billion guesses/second): 1.26 minutes
• Cracking offline, using massively parallel multiprocessing clusters or grid (one hundred trillion guesses per second: 0.0756 seconds

10 characters: Possible combinations: 171.3 sextillion (171,269,557,687,901,638,419; 1.71 x 1020)

• Cracking online using web app hitting a target site with one thousand guesses per second: 54.46 million centuries.
• Cracking offline using high-powered servers or desktops (one hundred billion guesses/second) 54.46 years
• Cracking offline, using massively parallel multiprocessing clusters or grid (one hundred trillion guesses per second: 2.83 weeks.

Take Steve’s advice: go for 10 characters, then add a symbol.