Traffic from parked domains. How is it possible?

[depi]

Hello,

I wonder how is it possible to get traffic from parked domains? I have not bought any PPC ads and I've got some hits from those sites.
Are they just some referrer spam? If yes I don't see it very effective for those spammers as only webmasters can see it.

What do you think about it? Anyone experienced the same?

[pubdomainshost.com]

Haven't seen traffic from parked domains yet ... Not sure how you got it.

Thx