How to use more than 3 adsense units

I see many blogs doing perfectly well by implementing 5-6 adsense ads unit on a [age, however as per adsense policy we can't use more than 3 ads units. Any idea how these guys are doing so without getting adsense ban. I have heard that using iframe is banned by google and very risky these daysm not sure if these blogs using iframe or there is some secret.

They're just running the risk. I their site is manually audited they will be banned.

Use 3 adsense units, then DFP to serve other banner spots with adsense backfill activated

Are you sure that they are using more then 3 AdSense Ads? Because there are a lot of websites that are using other ad networks with adsense together.

That's the reason why I am asking if they have only AdSense Ads. If they implemented more then 3 AdSense Ad's they will lose their account sooner or later because it's not allowed for us publishers to use more then 3 Ads per Site.