what does a strange item in "shared" on my sidebar mean?

Forgive me if I sound like an utter novice... but I am one. I have a Mac mini running OSX Yosemite 10.10.5. A few days ago I noticed a strange item appearing under Shared in my sidebar which seemed strange to me as I have sharing completely turned off. The icon is a sphere and the name is listed as w25.b.cap. I don't know what it means or what to do and I hope someone here can help me. Thank you and my apologies if it's a really silly question.