What Are they?

A spider or spyder as it is sometimes called are programs that sit on the FWP server and search out contraband. Be it anti-ad code. Flesh-Tone pictures ;) or files that are not linked to anything else. I sign that someone is using there acount for storage. (against MOST FWP TOS/TOU). Some even scan for large files and files of certain types (.exe, .zip, mp3). They work on there own. And at the end of the day when the sysop (systemsop) checks the record. All the files that have been flagged are looked at by a human. If they find that you ar indeed braking the TOU then you will be kicked off of the server, your files deleted, and most times without any kind of warning.

How To Avoid Them

To know how to avoid them you need to know what they look for. For example, if you were trying to hide your huge collection of .jpgs ;) w/o them knowing, you would use a different method then hiding your ad killing script.

Most spyders look for a few key elements. File size, file type, # of links pointing to the file, and at times certain other things. For example most servers flag all flesh tone (pr0n) picture files for later human review.

Hiding Files 1

Before you even think about dumping files into the account, you will have to set up at least an index.html page so you appear to serve some worthwhile purpose to the FWP, as well as gets rid of the telltale "Directory listing of /" that otherwise showcases all your contraband files. It doesn't have to be anything too elaborate, a simple "newbie page" will suffice for now. Newbie pages are cheap, slapped-together-in-15-minutes homepages typical of new Web writers who haven't fully mastered HTML or decided yet what their site's going to be about. Pictures of your pets, useless personal trivia ("My favorite colour is purple, I have a goldfish named Silver and I like spanish olives..."), "under construction" logos, complex email-me animations (stolen, of course) featuring letters folding themselves into paper airplanes and being swallowed by mailboxes or whatever, a handful of broken/outdated links and a low/broken counter are priceless earmarks of newbie webpages. If you want to keep the account more permanently, consider crafting yourself a small, content-containing website on the subject(s) of your choice ("deformed Alaskan bullfrogs", etc.), of maybe 5 interlinked pages or so, that you can upload as cover for any filez account you create.

Hiding Files 2

Most, if not all, FWPs require that every file you have be linked in an HTML document; this is to keep leeches like you from using your account as your own personal storage locker for large files. There are most likely some kind of automated spyder processes that go around looking for unlinked files. Additionally, most FWPs explicitly forbid private or password-protected pages. Despite this "full disclosure" policy on your account, it's still easy to keep your files relatively private while not technically breaking any of the rules regarding private files.
The ol' Link trick: Say I made a really long, innocent-looking link to any old page on my site. Suppose this link stretched accross one or two lines! A normal websurfer would click on it (or not) to get whatever page it links to, and think nothing of it. But, look carefully at this link. Run your mouse all over it, and see if you notice anything odd about this link. Did you find it? If not, click on the "t" in "two". Surprise! You might have found it because I told you to look for it...but do you think any old slackass surfer would've noticed? Statistically, the odds of a surfer clicking in the right spot by pure chance are near nil. There are of course some general pointers for using this trick successfully: Set your link, vlink and alink to the same colour! On most pages, virgin links are blue in colour and ones that have already been visited turn purple. So, if your surfer clicks that link, and all of it turns purple except for one letter, this obviously blows your cover. If you want to get really fancy, use a Javascript OnMouseOver command to further camouflage your hidden-file link. For this you just make your hidden A HREF tag as usual, and add the necessary JavaScript to the tag to make the hidden link behave just like the one it's hiding in. Your completed tag would look something like.

<A HREF="hiddenfile.zip" onMouseOver="parent.window.status='http://same_text_as_other_link';return true" onMouseOut="parent.window.status=' ';return true">

If you don't know how to use JavaScript, you can just stick to the links; it's fairly well hidden as it is.