Multiple LEDS multiplexed not burning out board pins?

Using Arduino LEDs and Multiplexing
1

I started a project to control 9 with 6 pins and ended up controlling 18 with the sample 6 pins.
I used no resistors between the pins and the LEDs.

Should the poor Aruino board burned up?

After getting the first 9 LED to work I added 9 more in the same configuration except reverese polarity and changed mode on the non-used pins; pinMode(nonUsedPins,INPUT);

Each pin is used in a matrix style fashion where 3, 4 & 5 are rows and 6, 7 & 8 are columns.

I'm curious why did this work without damaging the board?
thx Russ.

2

Post the scematic & code & link to the LED's datasheet.
Likely your on-time is limiting immediate damage, and long term failure hasn't occurred yet.