Communications satellites operating in 36,000 kilometer high stationary (geosynchronous) orbits are increasingly victims of jamming. There is a solution for military users, who can use existing anti-jamming technologies like frequency hopping and DSSS (Direct Sequence Spread Spectrum) on the sending and receiving end. But all users of civilian satellites cannot be equipped with these anti-jamming devices. The satellite operators can use this stuff for the control signals (going to and coming from the satellite) and that is increasingly becoming necessary. Note that jamming reduces the amount of data that can be sent, which is a serious, and expensive, cost for communications satellites.
Meanwhile, the jamming of civilian users grows, usually as part of a state censorship program. For example, late last year Syria and Iran were accused of jamming news service by BBC, France 24, Deutsche Welle, and the Voice of America, via radio and satellite, directed at Iran and Syria. This jamming was apparently in retaliation for European communications satellite operators refusing to continue carrying 19 Iranian TV and radio channels (as part of the growing embargo on Iran). Syria and Iran denied they were jamming but there is ample evidence that the jamming is coming from those two countries. Over the last decade the U.S. has developed equipment and techniques for locating the source of jamming with considerable accuracy.
Then there is the increasing number of incidents of space satellites being "hacked". It turned out that this was actually just an increase in the number of satellites up there and the number of ground stations broadcasting information up into the sky. Most of these "hacks" are just satellite signals interfering with one another. Same with cases where people believe their GPS or satellite communications signals are being jammed. On further investigation the real reasons tend to be less interesting and a lot more technical. All this usually has a large element of human error mixed in. But the recent problems with signals directed at Iran and Syria appear to be jamming.
But all this accidental jamming only demonstrates how easy it is to do it on purpose, and there have been several examples of that. In response the U.S. Air Force, which has taken the lead in developing electronic tools for attacking and defending satellite communications, and the satellites themselves, has been training people to attack and defend space satellites. This effort involves figuring out new, or improved, ways to jam satellites. Then you keep that stuff secret, in case potential enemies have not figured this out themselves. Next, you work on ways to defeat the weapons developed. Most of this is playing around with the signals themselves. You can un-jam a jamming signal with another signal. However, a lot of trial and error is required and you want to get that done way in advance of any actual war. When you do have to use this stuff for real, you have to expect that the enemy may well have come up with some angle you missed. Thus, there will be some rapid improvisation, and you will have more time and resources for this if you have worked out ahead of time the details of disasters you have already anticipated. No one is releasing much information about this, for obvious reasons. There won't be much discussion from any government, unless there is a terrorist attack using these techniques. That's yet another thing to worry about. There have already been such attacks in China, by a banned religious group, and elsewhere. It can be done, it just isn't easy and it's not getting easier.