I also did not mean attacks, but stealing from the oil/diesel/gasoline that flows through the pipeline. It is not so difficult once you get access to the pipeline, and the chances you will get awaw with it are big. As we know fuel is likely to become very precious with time...

We had several such cases in Bulgaria even though there in not that much pipeline network. Not to mention about the electricity being stolen by people, mostly from the poor minorities - the amount is in the range of tens of millions kwth yearly. You would think it is dangareous and you would be right, but the thiefs get better and also better-equipped with time.

It is amazing what people do when energy is scarce or they can not afford it.

Yup.  If it comes to that, I'm not really expecting there to be any oil or gas in the pipelines.  It will be like it was after Hurricane Katrina.  A few hours or days of panic buying that sucks the system dry.  Then oil and gas distributed in tanker trucks, surrounded by a platoon of armed guards.
This from 6th CONCAWE pipeline seminar 2002,

"
Theft or attempted theft from pipelines has been a
consistent feature of operations, particulary in
Eastern Europe, over a number of years and a major
cause of incidents. A recent case in Italy unfortunately
led to the death of the perpetrator. One
presentation described the measures being taken in
Hungary to address this problem. Between 1992
and 1999, the Hungarian system was attacked more
than 100 times. Although not all of these attempts
were successful, the value of fuel lost was substantial.
Even more expensive was the cost of clearing
up the spilt oil. To counter this threat, a sophisticated
leak detection system has been installed. This
not only detects leaks, but also pin-points the position
of the leak which facilitates rapid intervention.
As a result, the number of attempted thefts has now
decreased dramatically.
"