Use ctrl+shift+f to search through all scripts, click the .* icon (this turns on regular expressions) and search for each of the following:

• require\s*\(\s*\d
  • This will find things like require(152321) - though I've seen a few legitimate admin scripts use these, if you don't recognize it or didn't intend to install it, delete it!
• getfenv
  • This is another potentially legitimate function, but it's rare. This is typically used by malicious scripts to use the require function without spelling out require (so that you can't find them as easily).

Also:

• If type in the Filter workspace bar in the Explorer window, you can trying looking for a few common names (but this is not reliable, and you're likely to find legitimate scripts this way too): Fire, Anti, Virus. Many virus scripts are just named Script; some even have a blank name.
• If you ever find it in a script that looks like it only has one line, or looks like it's just a comment, or only has blank space, check the scroll-bars -- it probably has code that's hidden far off-screen. Any script that attempts to do this is malicious. (Note: just having scrollbars isn't the problem, it's when it's trying to trick you into thinking there's nothing there.)

Have you tried Ro-Defender plugin, it's a roblox anti-virus which scans all the models in your game to find suspicious scripts, it might work for the situation your in.

There are loads of different random Ro-Defenders, this is the one I use and it works fine: https://www.roblox.com/library/142273772/Ro-Defender-Plugin-v8-7

If you have any suspicions about viruses, be sure to watch the console. Since the moderation of the get actively fixes such viruses, they can issue various errors to the console. It is enough to start game testing mode, click on the error, and script should appear. Exit from the game test, right click on script -> Show in Explorer and delete him.

I Suggest A Couple of Things.

1:Disabling HTTP Requests.

2:Turn ThirdPartySalesAllowed Off.

3:Look Through The Workspace Like @chess123mate suggested.

Common Terms Are Virus, Fire, Script

Some Are Completly Random Named So Like

EXAMPLES OF WHAT MALICIOUS SCRIPTS ARE NAMED

I am your new lord lolz. reallylongscriptname pretty much just nonsense.

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Tell the owner to check his plugins, Also, Search up for "Script" in the Searchbar, it will show every script in the game.