A chain is only as strong as its weakest link.In terms of blogs with multiple owners, each individual owner becomes one link, in the chain of blog security.
Any blog with multiple administrators ("owners") is subject to its abuse by any one of the owners. Whatever the abuse involves
- Installation of dodgy code.
- Dodgy installation practices.
- Addition of untrustworthy members or administrators.
- Theft of the blog by removing all other administrators.
Any one administrator can install malicious code, can use an EZ Install procedure to invite a hijacked Blogger account, can add another administrator who can do any of these things, or can even remove all other administrators. Just one person (the "weakest link") can cause chain breakage (a damaged, hijacked, spam locked, or stolen blog).
Blog authors can also cause problems - either with dodgy links or posts.
You simply must choose your administrators - and team members, with great care. Blogger cannot intervene in internal issues which involve team membership.