Did you ever go out to your mailbox and get a handful of junk mail? Well, that is basically what SPAM is. SPAM filters work to cut down on the amount of junk mail that arrives in your e-mail inbox. But, it will not block spam if it is posted in a message on a forum.
Forum spam is the creating of messages that are advertisements, contain content contrary to the community rules or policies, or otherwise unwanted on Internet forums. Most forum spam consists of links to external sites, with the dual goals of increasing search engine visibility and generating more traffic for these websites. Some of these links contain code to track the spambot's identity if a sale goes through, when the spammer behind the spambot works on commission.
Spam posts may contain anything from a single link, to dozens of links. Text content is minimal, usually innocuous and unrelated to the forum's topic, or in a very old thread that is revived by the spammer solely for the purpose of spamming links. Alternately, when links are not allowed in the text of a post the spam links are posted in the user's signature where it is more likely to be harvested by search engine spiders than discovered by forum administrators and moderators.
Spambots are automated computer programs or a script designed to assist in the sending of spam. Asking a user to verify that they want to revive an old thread makes it more difficult for spammers to use spambots.
I am sure that is more information than you probably wanted to know - but it explains for you, and anyone else reading this thread, why they get that message when reviving an old thread, and why we have restrictions on new members posting links of any kind for their first few posts.
"It ain't what you don't know that gets you in trouble. It's what you know for sure that just ain't so." - Mark Twain