The British Government has for the second time failed to adequately redact sensitive information in a online report.
The Ministry of Defence failed to protect sensitive information about weaknesses in its radar systems when it used black highlight to hide text.
The document was replaced with a secure version.
The gaffe came six months after the Defence Department made the same mistake and failed to redact highly sensitive information on its nuclear submarines.
It exposed information on how a reactor meltdown could occur on the submarines, and information on US vessels, the Daily Star reported.
Sophos consultant Graham Cluley said in a blog that the mistake was "another schoolboy error".
“To make such a blunder once is unfortunate, to do it twice is careless in the extreme.”