As you can see here:
http://hugealice.nem.ninja:7890/account/get?address=NB6PQZBMF5DG7KQ3SU66C2WRFMKLSVPONEPZD6GB
this account is indeed a multisig. With 1 cosignatory being: NAZXEMKDB3IQK4NU2CX6RHIQD342W2AOKRYAAJV3
If you are not the owner of this cosignatory account, ask yourself: how could he have gotten your private key?
- is your account a brain wallet ?
- is your computer maybe corrupted ?
With 1), keep in mind that anyone can create your private key out of your password.
With 2), a hacker could have leaked your private key.
If you are the owner of this cosignatory account, you must issue transactions using the cosignatory for the multisig. Multisig in NEM implies that cosignatories control the account.