Study: NetSPI’s Top Password Masks for 2015
Date: January 19 2016

Percent of unique, cracked corporate passwords matching a character mask. Top 10 popular masks:

5.45%	ULLLLLDD
4.14%	ULLLLLLDD
3.10%	ULLLLLLLDD
2.91%	ULLLDDDD
2.79%	ULLLLDDDD
2.72%	ULLLLLDDDD
2.34%	ULLLLLLD
1.98%	ULLLLDDD
1.72%	ULLLLLLLD
1.51%	ULLLLLDDD

PasswordResearch.com Comment:
L = Lowercase, U = Uppercase, D = Digit, and S = Special or Symbol. So the password "Spring15" would have a character mask sequence of ULLLLLDD.