Invisible backlinks from homepage?

Today I checked the backlink profile of one of my competitors, and I found lots of backlinks come from unrelated websites. All of them are stuck on the top of the homepage but invisible. I only find them on HTML code.

All of these websites are real. I think the owner doesn’t know their website have these link.

Does anyone know how my competitors do this?

Homepage links sellers use different methods to hide links from regular users but this one doesn't look sophisticated to me, so it's either a links seller who's bad at programming or these are hacked links, you can PM the link of the website so I can have a better look at this.

MasonF said:

Homepage links sellers use different methods to hide links from regular users but this one doesn't look sophisticated to me, so it's either a links seller who's bad at programming or these are hacked links, you can PM the link of the website so I can have a better look at this.

Click to expand...

Thank you, PM sent.