Check Your External Links with This Tool
Incoming links (i.e., links from other websites pointing to your own) usually cannot hurt your search rankings, even if they come from spammy websites. This is because Google knows you can’t control those links.
Outgoing links, however, can get you in trouble, because you are in direct control. If you link to malicious or spammy websites, Google might put a red flag on your website and reduce your search rankings temporarily, until it figures what is going on. This why links on blog comments have the nofollow tag by default.
Sometimes if you link to a website that links to malicious or spam content you can also get in trouble, so it’s a good idea to keep an eye on the sites you are linking to. One tool you can use for this purpose is called Text Link Checker.
You just need to insert a URL (i.e., the homepage of the website where you want to analyze the external links), and the tool will start crawling all the links, up to three levels in depth if I am not wrong. After that it will build a little report with icons highlighting dangerous links.
Obviously you should use this tool only as a starting point of your analysis, because there are many false alarms. It’s a useful thing to have on your tool-belt, though, so check it out.