Back in July, satellite broadcasters transmitting television shows to Iran found their signals being jammed. The source of the jamming was quickly traced to Cuba. A satellite signal is very difficult to jam as it comes down from the satellite. But if you are close to the ground station that beams the signal up to the satellite, you can more easily interfere with that. At first it was thought that the Cuban government, using an old Soviet era electronic eavesdropping facility outside Havana, were doing the jamming as a favor to Iran (which buys Cuban support with supplies of cut rate oil.) The Chinese now run the old Soviet facility. The Cuban government denied it had anything to do with the jamming and said it would find out where the jamming was coming from, and they did. By August 20th, the Cuban government reported that they had traced the jamming signal to a suburban compound owned by the Iranian embassy. The Cubans ordered the jamming to stop, and it did.
But this incident has brought up an old Cold War fear, that some future foe would attack our satellite network and cripple our military and economic power. This is even more the case now, than it was in the 1980s (when it was a big, big thing.) Today, the military's dependence on satellites is much greater. Right now, the American military could fight without satellite support, but would do so much more slowly and with more dead Americans. So all those anti-satellite nightmares from the 80s have returned, as has the same lack of reliable ways to defend satellites. The basic problem is that there are more ways to screw up a satellite than there are to protect it. Something as subtle as releasing some sand in the path of a satellite will not only cripple, or destroy, the satellite, but it will look like a natural event. There are a multitude of sand size objects up there in orbital space, and getting hit by a grain or two is an accepted hazard when your put $200 million satellite into orbit.
There are less subtle weapons, like a small nuclear weapon. The burst of radiation and magnetism does a real number on satellites. And then there's old standby, the "KillerSat", a satellite that maneuvers close to its target, and then explodes. More sophisticated KillerSats can now use powerful lasers or various types of small missiles. It's also possible to get, one way or another, the access codes the ground controllers use to make the satellite do whatever it can do. Some satellites can change orbits dramatically, others can just be turned on or off. But most have enough mobility to allow ground controllers to order the satellite to move lower and burn up in the atmosphere (to "de-orbit.")
The U.S. is the biggest user of satellite technology, and thus the most vulnerable. China publicly discusses attacking America's satellite networks in any future war. This is scary, because at the moment it's easier to attack satellites than to defend them. Out of this has come the popularity of using more minisats (smaller, cheaper satellites.) A minisat is a bit harder to hit and easier to replace. It's understood that any attack on a nations satellites is an act of war. This is why many of the attack methods under discussion aim to make the damage look like a typical space accident. But if you can prove a specific nation is attacking your satellites, the first thing you go after are the enemy's satellite launching capability. At the moment, the attacker appears to have the advantage. But until someone actually tries to attack satellites, we won't know for sure.