Certificate: When you install some software, you need the support of certificate, but Nokia doesn't have a certificate to prevent the spread of mobile phone virus.

Signature: When installing the software, the certificate is bound to the software, which is called signature. Some software can't be installed without signature.

Brush machine: It is the same as changing the computer 2000 system into XP system, and it is the process of upgrading the whole system of your mobile phone. Brush machine is risky. If it fails, the mobile phone will not be used.