New guidelines to stop military personnel talking about their experiences have been introduced by the Ministry of Defence.
Playing multi-level computer games is also banned
Blogging and sending text messages about military matters is now banned without permission, the Guardian newspaper has reported.
It follows the row earlier this year when two members of the Royal Navy held captive in Iran sold their stories.
The MoD said it had just updated rules which already existed.
Personnel will also be barred from playing multi-player computer games and sending text messages, photographs and audio or video material without permission if they relate to defence matters.
The guidelines say "all such communication must help to maintain and, where possible, enhance the reputation of defence", the paper reported.
Receiving money for interviews, conferences and books which draw on official defence experience has now been banned.
The rules apparently also apply to Territorial Army members and cadets when they are on duty, as well as to civil servants working for the MoD.
But they have provoked condemnation from service personnel, some of whom immediately turned to online forums to talk about their incredulity and confusion about the clampdown.
An MoD spokesman said: "These are not new rules. These guidelines or similar have been around for at least a decade.
"They have been updated to reflect the findings of the Hall report on payment and authorisation of media contacts, and changes in communications technology - for example, the growth of the web."
The spokesman added: "Most public and private organisations of any size - in the UK and elsewhere - have rules on the authorisation processes to be followed before people speak publicly or to the media."
BBC News defence correspondent Paul Wood says that officials are worried about the constitutional implications of members of the armed forces declaring their views on policy or matters of controversy.
But they also frankly admit that they are losing the battle in the media on several key issues, our correspondent added.
Last month, the MoD's media strategy document - written by the senior civil servant in charge of communications, Simon McDowall - was leaked.
Based on the MoD's own research, he concluded: "There is a growing perception that, particularly on operations, our armed forces are not as well-equipped as they should be and that we do not look after our people as well as we should."