Stickied
Here's a list of useful links which will help you check cheats (exe's/dll) before running them.
All programs are freeware.
Hack Scanner - Steam Edition
http://www.mpcforum.com/showthread.php?t=162175
-Will scan files for Suspicious strings and API Functions related to account stealing. It will also decompress files compressed using UPX.
FileAlyzer
http://www.safer-networking.org/files/filealyz.exe
A tool to analyse and display file contents.
Jotti's malware scan
http://virusscan.jotti.org/
Online individual file scanner.
Resource Hacker
http://www.angusj.com/resourcehacker/
Allows users to modify 32bit Windows executables, doesn't work on all files
Hex Editor XVI32
http://www.chmaas.handshake.de/delphi/freeware/xvi32/xvi32.htm
A simple hex editor.
OllyDbg
http://www.ollydbg.de/
Other hints
Search the file name on google, it may bring up relevant information regarding the file
Scan it with your own virus scanner and ad-aware/spybot/windows defender etc
Get your friend to test it first, lol
Send it to yourself using a free email service which has a built in virus scanner
If it's a cheat, try it offline so any account information cannot be sent anywhere.
If a program is compressed/packed up and you can't find any information on it, you better off not running or unpacking it first, FileAlyzer can tell you what files are compressed with.
Hope this is useful, especially to cheat verifiers at The Fork Guild