The MyBlogLog service, owned by Yahoo nowadays, was exploited to spam its users this weekend. There was a hole in the invite to co-author system, and it was promptly used. A lesson hard learned for the team, as can be read in a recap blog post.
This is not the first time MyBlogLog is spammed, but at least it didn’t affect the actual MyBlogLog widget on the sites using it this time around. It’s one of the problems of using hosted services like this. People can use it for bad things, and there’s nothing you can do about it.
That’s why you should always consider hosting your own solutions. Sure, they can break and be exploited as well, but at least you’re in charge.