The use of the term "viral" is generally considered inflammatory and unhelpful. An uninformed reader might be led to believe that the act of linking with GPL software can somehow "infect" proprietary software, causing it to be open source. This is incorrect. The GPL restricts distribution (i.e. the combined work may not be legally distributable to anyone), it doesn't "infect" things.
"Viral" was the only word which sprung to my mind when looking for the right word. And personally I think viral is a mostly neutral word (see viral marketing) which describes the situation. Would "share alike" be a better word perhaps?
But isn't LGPL is copyleft too, but not viral on linking. The only reason I used "viral" is because that is the clearest word I could think of, and still is.
