-# ver: allow versions up to 99.
-# usr (in case ver didn't work):
-^(ver [0-9]+ msnp[1-9][0-9]? [\x09-\x0d -~]* cvr|usr md5 i [ -~]*)
+
+# First branch: login
+# ver: allow versions up to 99.
+# I've never seen a cvr other than cvr0. Maybe this will be trouble later?
+# Can't anchor at the beginning because sometimes this is encapsulated in
+# HTTP. But either way, the first packet ends like this.
+# Second/Third branches: accepting/sending a message
+# I will assume that these can also be encapsulated in HTTP, although I have
+# not checked. Example of each direction:
+# ANS 1 quadong@hotmail.com 1139803431.29427 17522047
+# USR 1 quadong@hotmail.com 530423708.968145.366138
+
+# Branches are written entirely separately for better performance.
+ver [0-9]+ msnp[1-9][0-9]? [\x09-\x0d -~]*cvr0\x0d\x0a$|usr 1 [!-~]+ [0-9. ]+\x0d\x0a$|ans 1 [!-~]+ [0-9. ]+\x0d\x0a$
+