In an online discussion, Google's John Mueller said that links from other websites can hurt your own site (despite of what Google said in the past): "Looking back, I don't believe I've seen a site that was clearly in a bad position only because of third-party activity (such as getting links from bad websites). Theoretically, it's probably possible (which is the reason for the 'almost'), but in practice, we have a lot of safeguards that help our algorithms to evaluate sites in useful ways. Our algorithms are pretty complex, it takes more than a handful of bad links to sway their opinion of a website." This means it is important for all of us to check which sites are linking to your sites. One of the better tools for this is this backlink checker. Try it out for yourself Know who is linking to you!
LoL come on man don't try to scare us with mislead interpretations. John Mueller, in that discussion, is telling us that there's no need to worry about competitors building spam links to our websites, and you draw the opposite conclusion. You could have advertised for your backlink checker tool in a more elegant way, no offense intended..