Can Competitor Hurt My Website Ranking?

[Die Hard]

Hi all,
Actually, I want to know that can competitor hurt my website ranking. I am seeing, somebody is doing negative activities for my website. Before three days ago I have checked my google webmaster account. I have seen that, there are more than thousand 404 pages in the account, and then I have checked that, from where am I getting these links (404 links)?    There were lots of classifieds sites, where somebody posted my website link wrongly (put broken link). I had got this site emoment.net, which has 5018 links to my website and total links 17028, i have in google webmaster account. I am still safe; I have not got any negative effect till now. But i am confused, Will I take it seriously or ignore?

[ljennifer012]

Not all 404 mean error or bad URL

[arold10]

Why posting the same thing on different forums? I saw a post similar to this one Webhostingtalk.

Some webmasters often mention that your competitors may do something that can hurt your ranking, but I've never heard that something like that really occurred. I think it's best to outrank a site by using proper search engine optimization methods, instead of trying to destroy someone ranking so that you can get ahead of him/her.

[emmawilliam87]

Yes they do so. But if you daily check your website on-page and off-page, so it won;t matter whatever they do.

[e@buzz]

No thats not possible there will be some problem or error like bad URL.