By Martin Asser
BBC News, Jerusalem
Militants closely monitor military web postings, Israel believes
Israeli defence chiefs have moved to tighten internet social networking rules after photographs appeared showing sensitive military subjects.
A review of Facebook pages belonging to Israeli troops found that some had posted detailed pictures of air bases, operations rooms and submarines.
"These are things we don't want the public to see for security reasons," an official source told the BBC.
Posting photos of troops in uniform - a popular pastime - is still allowed.
The new set of rules - which has not been made public - includes a ban on images of pilots and members of special units, and anything that shows specific military manoeuvres.
Rite of passage
The defence ministry launched its inquiry earlier in the year to check the potential security risk in the dozens of social networking groups dedicated to life in the Israeli military.
Compulsory military service is a rite of passage experienced by large numbers of young Israelis and in recent years they have shared their experiences through photos and web-posted accounts of their activities.
Posting photos of troops in uniform - a popular pastime - is still allowed
"There's a lot of illegal photography inside the Israeli Defence Forces, including the Israeli Air Force," a source inside the air force told the BBC.
"Most of the soldiers don't understand how much damage it may cause," the source added.
Militants in Lebanon and the Palestinian territories are believed to monitor Israeli web forums and communities, including Facebook and the photo sharing site Flickr, to get information.
The military source, who cannot be identified, says a few of his comrades are authorised to take pictures at their bases and to post them on Flickr.
Every photo is vetted by military censors, and the ones considered appropriate are assured a warm reception by the many enthusiasts of military hardware in the online photo-sharing community.
But the defence ministry says military tribunals have investigated and disciplined about 100 soldiers who broke the rules and unwittingly helped the enemy this year.
It may seem a large number, but the defence ministry source said: "Considering the number of soldiers there are with social networking websites, it is a tiny proportion."
The worst offenders were punished with a month in jail for particularly egregious posts, while others were warned they would face similar punishment if they re-offended.