Spam occurs if identical pages are suggested to the same category multiple times, if one site is suggested to multiple inappropriate categories, if an unlistable site is repeatedly suggested, if multiple unlistable sites are suggested by the same submitter, if inappropriate deeplinks or subdomains are suggested, or if a suggestion otherwise violates our Submission Policies or disrupts DMOZ. Definitions of sites that are usually not listable in the directory can be found at Sites Generally Not Included. The use of auto-submission software is always considered spam.
Another form of spam is Update Spam, where a person or business repeatedly asks for updates to a listing, either for minor changes to the URL, title or description, or to keyword stuff the listing. A variation on this is that the person requesting the update is not doing so in the particular site's interest, but to get the listing removed or replaced with another, which is why the suggested change must be visible on the original site.
One trick that sites will use to try to get multiple listings in the directory is to suggest their site (or similar versions of their site or sub-sections of their site) under different registered domains. For example, "Mozillas for Sale" might suggest both mozilla-sales.info and a different URL, mozilla-sales.biz, that leads to the same page or same basic content.
Some suggest multiple deeplinks of their sites. In a few selective cases, sites will be deep-linked. In these cases, the deep links should offer content that is extremely useful to a particular category, and the content should be unique. Deeplinking should be the exception rather than the rule.
Submitters and sites that repeatedly or persistently spam the directory will be blocked from suggestion, and their sites may be removed from the directory. Sites affiliated with known spammers may also be removed from the directory and/or blocked from suggestion.
If an editor notices spam or multiple unlistable sites in a category and/or its unreviewed queue from the same source, then they should go to this forum internal thread to ask that appropriate action be taken.