Method 1
- For Windows XP and 2000 users, open and copy from the following location:
C:\Documents and Settings\All Users\Application Data\Malwarebytes\Malwarebytes' Anti-Malware\rules.ref
- Windows Vista and Windows 7 users, open and copy from the following location:
C:\ProgramData\Malwarebytes\Malwarebytes' Anti-Malware\rules.ref
Method 2
Download a manual definition updater here