Not many new begginers/new players know, so I'll share it to those new players. You can only, so far, encouter hacker/cheater/modder in only GTA V Online, not offline/single player. So if you come across player behaving strangely, report them. It won't do them any harm if they're innocent anyway!

• 1.Pause the game (press ESC) and navigate to the “ONLINE” tab.
  
• 2.Select “Players”, and choose the name of the player cheating.
  
• 3.Select “Report”, and confirm your report with the “Exploit” category.

Source:
https://support.rockstargames.com/hc/en-us/articles/200704406-How-to-Report-Cheaters-in-Grand-Theft-Auto-Online

Actually it's a matter of your choice. I've met a friendly modder and made a video with them (click here to watch the video) . He was friendly. I also met abusive hacker/modder/cheater who kills me instantly with only one shot.

"Any attempt to tamper with the behavior of GTA Online by installing or executing mods, scripts, or other exploits, modifying the game files or manipulating the game in any way while it is executing will result in disciplinary action including but not limited to time in the cheater pool, bans and potential suspension of your account. "

Source: Rockstar Games[www.rockstargames.com]

So, in any way, using mods or doing you're not suppose to do in GTA V Online will result in "punishments" or as what Rockstar said, discplinary action.

If you met one, report them immediately.

1.) Cheater/modders can take your money away, or damage/harm you in negative way. Other example: they can instantly killing you, exploding cars that result in money loss because you need to replace them, forcing you out of the car so that you can't use your car to reach your destination,etc.
2.) Modding is not allowed in GTA V Online.
3.) Disturbs other player

• Create your own private session
  
• The more players in public session, the greater the risk having one hacker masquerading as normal players. So invite your friends to your own session/join your friends' session.
  
• If you find hacker, it's recommended to FIND ANOTHER session immediately. Press ESC -> Online -> FIND NEW SESSION.

You can easily find in youtube : GTA V Hacker / Modder and learn how to spot one.
Here's my references to you:

Modder that spawned objects













Modder/cheater that uses godmode (unkillable):


































Modder that gives you money (Rockstar Games will not ban you if you receive it unwillingly and will reduce your money to normal.)











And many more on YouTube. Stay safe, be vigilant. If you see one, just leave the channel.