Schwarzarbeit is the phrase that a German would use....for people working under the table (not being taxed, not paying into social pension, not getting required health-care taxation, etc).
Generally, you will see joint efforts between the Arbeitsamt, the German Customs Office, and the German Police.....to conduct raids in urbanized areas. Twenty years ago....it was mostly at construction sites and brothels (yeah, it's amusing to note these). There were usually reporters with the sting-operation and they'd write up some kind remarks about the local government doing something about 'black-work'.
Today? There are various other segments of society where these government teams check out....from garage operations, to restaurants.
No one really has any idea how many illegal 'black-workers' exist in Germany. It could be 100,000.....it could be 500,000. These are people without a visa, without healthcare, and without any pension deal going on.
I sat last night and watched a public-TV news segment where they were interviewing this guy....masked for the interview. He was a janitor....being paid roughly a thousand Euro per month. I assume he was in a crowded apartment with five or six other guys....in the same situation, with one legal guy renting the apartment or just a apartment owner letting them stay for cash under the table as well.
All of this is illegal of course.
Why do German businesses support this? Well....if you were the clean-up boss over forty buildings....you'd probably go out and hire half your crew in a legal way, and the other half for 40-percent less....just paying them in cash. The odds of the police-raids occurring after 5PM, when the clean-up crews go on duty? Probably a one-percent chance over a ten-year period.
Who makes up the various nationalities involved? Just about everyone from outside of the EU. Journalists hype up on occasion the Albanians in Germany and how they fit into this situation, but they are simply just one group out of dozens.
A career at this? The guy from the TV segment last night that I watched....noted only that he was sending back cash to his family in the 'homeland' (never noted as to where). He was in his mid-20's and I'd take a guess that he'd do this for twenty to thirty years.
A reflection upon German society? Well, here's the thing....for every real job, there's a governmental cost involved, from taxes, to social pension, and to include healthcare. Even if you were the gas station clerk from 9PM to 6PM.....your salary has a 40-percent burden to it. So it really encourages German bosses to find short-cuts and illegal ways to avoiding the cost burden. That's the simple description.