LinkedIN URL decoding

In LinkedIN, these codes, found in the URL (one by URL):

ACwAAAFX3cUB_8VkdrflK8rsvnKYiezfErHYgUA
ACwAAAEKW6UBiVnYhd5eRAV4ZnTD_exLPsFdl_8
ACwAAACBf2kBP6-WdZCP7ZYMusa_s-DIM1TksUQ
ACwAAAAK5kwBgLjKXRS19PWD8PjzNCTdldwPRuM

are going to be converted in user names.

Can anyone tell me if this is an encoding, encryption, hash or what? And how to 'decode' it?

I tried with base64, but I didn't get to a result.

Thanks!