Ennis made the suggestion that someone write a tutorial on Hijack this-

Sources (I used them a lot)
http://www.mjc1.com/mirror/hjt/
http://hjt.wizardsofwebsites.com/

What Hijack This is for, is to search key areaís of your computer that are commonly used to change your browsers settings. It doesnít scan them, it shows you everything, and itís your decision what can stay and what can go. Most of the entries Hijack This will come up with are legit, so it can make Hijack This somewhat tricky. You have to determine what stays and what goes.

Download Hijack this
http://209.133.47.200/~merijn/files/HijackThis.exe
If you have used ad-aware, spybot, or any other spyware removal software since your last boot, reboot your computer. Open it, click ĒconfigĒ in the bottom right of the window.
edit- Because of malware restricting access to the site, merjin moves the download links around. http://www.spywareinfo.com/~merijn/downloads.html

It should look like this when you run it:
http://www.mjc1.com/mirror/hjt/begin.png

Main settings:
Basic configuration Make sure safe mode and backups are turned on, as well as processes. Safe mode and backups will help you if you screw up.
Ignore list:
Used to help clean up your results. When you scan, you can ignore results you know are legit and they will be moved here.
Backups
When you fix entries in Hijack This, they will appear here as backups, given that youíre setting is turned on.
Misc Tools:
Generate Startup Log - Iíve never used it, but it does what it says. Shows you autoexec.bat and other things that boot up with your pc.
Uninstall
Check for update - I didnít even know that existed until nowÖ

The process!

Click scan in the bottom left corner, if you donít see it, click back in the bottom right corner.
Should look like this:
http://www.mjc1.com/mirror/hjt/fix.png

A whole bunch of crazy lookiní files will appear in the box above. About now, you have to start using common sense. If you see something like:
R0 - HKCU\Software\Microsoft\Internet Explorer\Main,Start Page = http://www.somekindapornsite.com/
Where the website shown is something you want nothing to do with, then check it. Basically, you just need to look for entries that look funny, google them, and see if they are commonly listed as a hijack or spyware.

Here is a section from http://hjt.wizardsofwebsites.com/
Two Letter Codes
After the running processes, the list of entries found by Hijack This begins. Each entry starts with a 2-letter code to say what it is. According to Hijack This' Info, heres what each code means:
R - Registry, StartPage/SearchPage changes
R0 - Changed registry value
R1 - Created registry value
R2 - Created registry key
R3 - Created extra registry value where only one should be
F - IniFiles, autoloading entries
F0 - Changed inifile value
F1 - Created inifile value
N - Netscape/Mozilla StartPage/SearchPage changes
N1 - Change in prefs.js of Netscape 4.x
N2 - Change in prefs.js of Netscape 6
N3 - Change in prefs.js of Netscape 7
N4 - Change in prefs.js of Mozilla
O - Other, several sections which represent:
O1 - Hijack of auto.search.msn.com with Hosts file
O2 - Enumeration of existing MSIE BHO's
O3 - Enumeration of existing MSIE toolbars
O4 - Enumeration of suspicious autoloading Registry entries
O5 - Blocking of loading Internet Options in Control Panel
O6 - Disabling of 'Internet Options' Main tab with Policies
O7 - Disabling of Regedit with Policies
O8 - Extra MSIE context menu items
O9 - Extra 'Tools' menuitems and buttons
O10 - Breaking of Internet access by New.Net or WebHancer
O11 - Extra options in MSIE 'Advanced' settings tab
O12 - MSIE plugins for file extensions or MIME types
O13 - Hijack of default URL prefixes
O14 - Changing of IERESET.INF
O15 - Trusted Zone Autoadd
O16 - Download Program Files item
O17 - Domain hijack
O18 - Enumeration of existing protocols
O19 - User stylesheet hijack

There is no need to memorize all of these, just read through them so you are familiar with what HJT detects.
Legitimacy Check

In the following sections, you will be asked to "check if a url is legitimate". This means deciding if it is a URL that user would want to visit, or if it is a likely hijacker. URLs that you recognize such as Google, Yahoo!, a news website, or a ISPs website are clearly legitimate items. They do not need to fixed. If you do not recognize an item-go the URL. If the site has unending popup traps, or is in the domain of a known spyware (eg coolwwwsearch.com, gator.com, new.net, etc) is not a legitimate item. Most hijackers are sponsored search engine/portal sites. Usually they are pretty easy to detect. If it is a portal site with tons of links packed into one page, with categories such as gambling, insurance, computers, and adult, you can bet its a browser hijacker that should be fixed. If it is a search engine with the words "Pay Per Click" anywhere fix it. If it is a search engine with several or many entries for it in the R* section of Hijack This, you can also bet that its forcing itself on the user. If your not sure, ask the person if they use that site or not.
R - Registry, StartPage/SearchPage changes
Any entries whos 2 letter code begins with R should be checked to see if the URL is legitimate. Throughout this tutorials I will say "check if its legit". To do this, use the "Legitimacy Check" rules at the top of this tutorial.
R0-Advanced Info
R1-Advanced Info
R2-Advanced Info
R3-Advanced Info
F - IniFiles, autoloading entries

Basically anything beginning with "F0" is bad and should be fixed. F1 entries can be good or bad. Google the filename to find out what it is.
F0-Advanced Info
F1-Advanced Info
N - Netscape/Mozilla StartPage/SearchPage changes

Items that start with N are related to Netscape. These are similar to the R entries. Follow the rules for deciding if a URL is legitimate. Netscape homepages are not hijacked as often as IE though.
N1-Advanced Info
N2-Advanced Info
N3-Advanced Info
N4-Advanced Info
O - Other, several sections which represent:

O1 - Hijack of auto.search.msn.com with Hosts file
01 entries are entries in the HOSTS file. HOSTS is a way of redirecting a URL to an IP. It can be used for ad blocking, speeding up internet access, or Hijacking. If multiple URLs point to the same IP address, fix them all (UNLESS THAT IP ADDRESS IS 0.0.0.0 OR 127.0.0.1). This shows up a lot
O1 - Hosts: 216.177.73.139 auto.search.msn.com
O1 - Hosts: 216.177.73.139 search.netscape.com
O1 - Hosts: 216.177.73.139 ieautosearch
They should all be fixed, see how it redirects all searches to 216.177.73.139 (type that IP in your browser for an example of non-legit page).
O1-Advanced Info

O2 - Enumeration of existing MSIE BHO's
The Browser Helper Object. Can't browse with em, cant browse without em. These are sort of plugins for the browser. Each has a unique, identifying number and a filename. Use TonyKlein's BHO list to check if each one is good or bad http://www.spywareinfo.com/bhos/ After a few logs, you will start to recognize which BHOs are safe (such as MSN Radio and NAV Antivirus). Note: any BHO with ClientMan Or Clien~1 in the filename should be fixed. Sometimes spyware tricks you into thinking its legit by using a safe-sounding filename. Check each BHO carefully!
02-Advanced Info

O3 - Enumeration of existing MSIE toolbars
03 entries are toolbars in web browsers. Most are harmless, but many bad hijackers add toolbars to the browser. If it is named "Yahoo Companion" or Google Toolbar, or something of the sort, its probably legit. You can find out what a Toolbar is at TonyKlein's list
http://www.spywareinfo.com/toolbars/
Any toolbar with a random-seeming filename should be fixed.
O3-Advanced Info

O4- Enumeration of suspicious autoloading Registry entries
Startups from the registry. Despite the name-many legit programs show up here. Ignore entries that you recognize to be from a legit program. Use this website to find out what the rest of the entries are.
http://www.pacs-portal.co.uk/startup...artup_full.htm
04-Advanced Info

O5 - Blocking of loading Internet Options in Control Panel
There is only one entry here, and it should be fixed. This entry stops the Internet Options from showing in Control Panel. It is used by Hijackers to hide themselves
05-Advanced Info

O6 - Disabling of 'Internet Options' Main tab with Policies
Internet Explorer restrictions. Unless you have used a security program to lock your browser settings, fix these. You won't know if the user has done this or not. You can ask them, but if they have a lot of spyware, its safe to say that they should be fixed.
06-Advanced Info

O7 - Disabling of Regedit with Policies
Restricted registry access using Windows System Policies. Fix this, unless you are using a computer where it may be there on purpose eg. lab/shared/school systems.
07-Advanced Info

O8 - Extra MSIE context menu items
Extra right click options. If you don't recognize it, search google. "Browser Pal" should always be fixed. Programs such as popup blockers or google toolbar often show up here.
08-Advanced Info

O9 - Extra 'Tools' menuitems and buttons
Extra toolbar buttons. If you don't recognize it as a legit program-search google. A simple search will usually reveal if its spyware.
09-Advanced Info

O10 - Breaking of Internet access by New.Net or WebHancer
Winsock Hijacks. Using old versions of Spyware removers can cause these problems! Spybot can usually fix them, or a specialized tool such as LSPFix.
O10-Advanced Info

O11 - Extra options in MSIE 'Advanced' settings tab
Extra Advanced Options group in IE Adds another group of options in the Advanced section of IE's Internet Options, which are stored in the registry. CommonName does this.
O11-Advanced Info

O12 - MSIE plugins for file extensions or MIME types
Internet Explorer plugins. Usually pretty harmless. Used by programs like Acrobat Reader.
012-Advanced Info

O13 - Hijack of default URL prefixes
Default Prefixes. Eviiil-always fix these. The default prefix (Stored in the registry) adds itself to the beginning of any URL where you did not enter the prefix. Default Prefix should be http://.
O13-Advanced Info

O14 - Changing of IERESET.INF
Reset Web Settings Follow the rules for checking if a URL is legitimate.
O14-Advanced Info

O15 - Trusted Zone Autoadd
Unwanted trusted zone site. This could be bad, but not many hijackers use them. The common one is free.aol.com. This entry can be fixed.
O15-Advanced Info

O16 - Download Program Files item
ActiveX Controls These are downloaded when you play an online game, use iPix, etc. If it is from a known game site such as Yahoo or Pogo, or the Macromedia site, its legit. Other items you can search for to find out. I usually just do a quick check over these items. Always fix them if they seem to be dialers, adult, or casino software.
016-Advanced Info

O17 - Domain hijack
Domain hijacks always include an IP address, do a WHOIS on the IP address. If it comes up with a legitimate owner (like an ISP or college) leave it. Otherwise, fix these entries.
O17-Advanced Info

O18 - Enumeration of existing protocols
Extra Protocols. These don't show up very often, but Google will tell you what they are. I have seen LOP and CommonName use them.
O18-Advanced Info

O19 - User stylesheet hijack
Style sheet hijack. I have only seen 1 hijacker use this. If the filename is default.css, it can probably be fixed. You may want to tell the person not to fix it if they are using a custom CSS file in their browser (these are often used by colorblind, or vision disabled users).
O19-Advanced Info
Donít remove things you arenít sure of. If you need help, post your log in the adware section of AO and some of us can help you decide what to remove.

All done