I see it it many tanks, particularly in fish shops for some reason. But like all algae, it's easy when you know how to nuke it. You'll find it growing on the edges of some plants, wood and filter outlets/inlets. Really difficult to remove and looks like the below.
How is it caused: In a high light, high CO2 tanks, it's caused by unstable CO2 levels. In low light tanks with no CO2, frequent water changes have been known to bring it on along with poor water movement.
How to get rid: In high light, high CO2 tanks making sure your CO2 levels are spot on will solve this problem (use a drop checker) and ensure water distribution is excellent (remember you want to see the plants swaying in the current). In low light tanks, use liquid carbon and fix your water distribution issues.
This algae will not die back so needs physically removing :( If you find it keeps coming back, you know you haven't fixed the above issues.