I left a Linux ISO (possibly Ubuntu) seeding on a lab computer at university, and forgot about it after I'd burned the DVD. You can see this was a while ago.
A month later an IT admin came to ask what I might be doing with port 6881. Once I remembered, we went to the tracker's website and saw "imperial.ac.uk" had the top position for seeding, by far.
Fortunately, it was the nice way — that university is one of the backbone nodes of the UK academic network, so the bandwidth use was pretty much irrelevant.
A month later an IT admin came to ask what I might be doing with port 6881. Once I remembered, we went to the tracker's website and saw "imperial.ac.uk" had the top position for seeding, by far.
The admin said to leave running.