On Jan 1, 2016 version 2.1 of this add-on was released to address an exploitable SQL injection vulnerability. If you are still using a version of this add-on which is below 2.1 or released before Jan 1, 2016 then it is essential that you update to the latest version of the add-on as soon as possible to fix this security issue.
Weekly Digest v3.4 changes:
1) Emails are sent only if there are new threads.
2) Phrase updated.
Weekly Digest v3.3 changes:
Added Image URL to Options. The email can now include an optional image such as a logo.
Weekly Digest v3.0 changes:
Added "Sent to Username" information to help identify who the email is sent to.