In case of blogger blogs, precaution is the only cure.
If someone has access to your blogger account password, he/she can do an unrepairable damage to your blog(s)
Here re some measures which you can take.
1) Keep your password highly confidential. There is no need to share it with anyone.
2) Make sure your password is strong and contains random letters, alphabets and characters.
3) Do a routine checkup of your blog. check source code of posts and make sure you dont find any spam link injection.
4) If you see a sudden fall in Your SERPs, try to figure out the reasons. Someone might have altered your blog posts and might have linked them to spam sites.