The blog, simply called Peerblog, was designed to show the candidate, not known for his mastery of social media, in a better light. A former journalist for the magazine Focus set it up to bring supposedly neutral authors onboard and portray Steinbrück positively - along the lines of US campaigns conducted in favour of but independently from election candidates.
Yet Steinbrück apparently failed to ask who was stumping up the six-figure sum to pay for their efforts, according to a Der Spiegel report - and the businessmen who had done so remained anonymous.
Parliamentary manager of Angela Merkel's Christian Democratic Union Michael Grosse-Brömer told the Hannoversche Allgemeine Zeitung: "Peerblog to me appears to be a special construct which begs the question whether here something is deliberately being put offshore where political party laws are concerned."
By Wednesday the parliamentary administrators had given notice they would take a careful look at Peerblog to check whether it constituted a form of undeclared party financing.
But unknown hackers were faster, and organised a denial of service attack, bombarding the site with so many requests for access that it collapsed.
The blog was killed on Thursday evening, leaving Steinbrück with a couple of problems, the Tagesspiegel newspaper reported on Friday morning. Apart from the lack of a blog being written in his favour, Steinbrück is again connected with opaque financing questions, a topic which has dogged him since his candidature was announced.