Update: As of April 2002, Gator has been implicated in a questionable practice some are calling "drive-by-downloads". In this scheme, a normal banner or popup ad will attempt to install software (executable code) on the user's PC. Depending on the browser's security settings, the software will either download silently and without any user action, or present an install dialogue. Novice users may choose "Yes" thinking the browser is asking to download a legitimate page-display plugin.

Gator is a software product that can automatically fill in passwords and other form-elements on Web pages. But its main purpose is to load an advertising spyware module called OfferCompanion, which displays pop-up ads when visiting some Web sites. Gator boasts that since it's software is always running, it can spam users with "Special Offers" and other ads anywhere they go--even competitors' sites--with remarkable targeting capabilities, since it can spy on what sites the user is visiting. Don't take my word for it, see what kind of abilities Gator boasts to potential advertisers.

Gator is confirmed spyware, according to Tribune Media Services (via SecurityNewPortal):

"Gator tracks the sites that users visit and forwards that data back to the company's servers. Gator sells the use of this information to advertisers who can purchase the opportunity to make ads pop up at certain moments, such as when specific words appear on a screen. It also lets companies launch a pop-up ad when users visit a competitor's Web site."

According to SimplytheBest Spyware information:

Gator helps you to fill out forms and remember passwords. Gator targets consumers based on site visitation and/or historical behavior. Your personal information is stored on your computer in an encrypted file. Gator accesses this personal information on occasion, using your IP address to help diagnose. Gator provides aggregate statistics about its customers, traffic patterns, and related site information to third-party vendors. In order to provide this service, they collect information on your web usage.

Gator recently sued the Internet Advertising Bureau for decrying their methods as unethical and deceptive, and potentially illegal. Gator is seeking monetary damages for the IAB's "malicious disparagement", as well as a declaratory judgment deeming their methods legal and forbidding the IAB from bringing their own suit on behalf of members whose sites' ads are being poached.

Ben Edelman, a Student Fellow at the Harvard Law School, has performed detailed analysis of the Gator/GAIN software as part of a pending legal case between Gator and sites it displays competitors' advertising on.

Gator Modules
 

Gator (iegator.dll and others)
Gator is the main software, which autocompletes Web forms (which is completely unnecessary for many users these days, since IE and Mozilla (and Netscape?) have had automatic form completion, password saving, etc. built in for some time.

OfferCompanion
This is the advertising spyware module. It is responsible for spying on your Web browsing habits, downloading and displaying pop-up ads, and transmitting (personal?) information to Gator.

Trickler (fsg.exe, fsg-ag.exe, fsg*.exe)
Trickler is an "install stub", a small program that is installed with the application you really wanted. (Gator almost always appears on your system due to installing OTHER software, and not the installer available from Gator's website.) When installed, Trickler inserts a Run key in your Registry so that it is silently and automatically loaded every time you start your computer. Trickler runs hidden and very slowly downloads the rest of Gator/OfferCompanion onto your system. It is suggested that this "trickling" activity is intended to slip under the user's radar, the steady, low usage of bandwidth going unnoticed.

While often named fsg.exe, Trickler can go under other similar names, such as fsg-ag.exe (installed with AudioGalaxy) or another name containing "fsg" or "trickler".

GAIN (GMT.exe, CMESys.exe, GAIN_TRICKLER_*.EXE, other files)
GAIN is short for Gator Advertising Information Network, and is the newest incarnation of the Gator spyware we all know and love. Gator describes this module here.

Dropping Gator

If you actually use(d) Gator for its purpose of remembering passwords, there are safe alternatives. The major browsers (IE, Netscape, Mozilla) and some non-major ones now include an autocomplete and password-remember feature. Gator users can also easily switch to RoboForm, a free program that does the same thing without spamming your system with ads and selling your privacy short. It can even import all your Gator data. Also, check out this page for retrieving passwords from the Gator software's database.

Links
ThiefWare - more information on these onerous products
Scumware - Software that is ripping webmasters off - list of active Scumware (TOPtext, Surf+, Gator...), how to remove them, and more.
Gator rushes to court over ad technology - Gator's lawsuit against the Interactive Advertising Bureau over negative statements, and request for declararoty judgement