I'm pretty sure one of my client's sites has been targeted by malicious black hat link building tactics employed by a competitor site. Over the last few weeks we've gotten 100s of super low quality spammy backlinks. No one has been doing link building, so the only thing I can think of is that competitor entered our URL into some spammy backlink building sites.

Has anyone else experienced this?

It's the real estate industry, so I wouldn't be surprised considering how competitive it is, but I'd love to hear your experiences.