If you encounter a player who you think is using hacks or cheats, grab the replay ID of the match from the History section of the main menu and it include it in your report. Be sure to watch the replay first and include the approximate time that the player can be seen using a cheat in the report as well.
NWI, you guys posted this on January 17. Reporting according to these instructions is still almost always impossible because you haven't fixed the History tool. It only records the first few minutes of a match so, if the incident you want to report happens after that, you're just out of luck.
Moral of the story: If you like to cheat, go ahead. It's generally safe to do so after the first 4-5 minutes of the match.