There are 398 game titles on Steam which make use of the Valve Anti-Cheat system (VAC for short), and should you be hit with the Banhammer, you'll be prevented from playing on VAC secured servers forever.
Sites and programs often claim to be able to get around VAC bans, and the below website is no exception.
They claim to have a "New, faster execution of server side PERL scripts" alongside "DDoS protection", and ask the would-be cheat ban bypasser to enter their Steam username then wait for their "New Steam reverse plugin version 3" to set about removing that VAC ban. Is this the part where they try to convince you that green text on a black background in a fake console box is equals cool hacking antics behind the scenes?
It sure is.
Of course, you don't tend to get something for nothing - and in this case, you get nothing for signing up to something instead. They want you to verify you're an actual human by, er, signing up to a selection of mobile deals at 9 Euros / 6.50 GBP / 9.90 USD per subscription.
Nothing above is going to miraculously unban your Steam account from a VAC slapdown. Once the ban is applied, that's it - no amount of downloadable mobile content or fancy looking console boxes will rectify that. Sometimes people get away with a bit of cheating, but as far as Steam goes the consequences are irreversible. Don't cheat, and you'll be playing on safe and secured servers for a long time to come.