Police raiding companies

I have a question.

I was always lead to believe that the only way that the police could bust you for working illegally in a school, is either to actually catch you in the act of teaching or find some evidence like a clock-in card, or if you are mentioned in the books.

However my case is different, I have been working in a small company in Hsin Tien for the last year. I am registered as a student in Chinese college but do this for four hours a day.
I do not pay tax but Human Resources run a tight ship so they have my details on record. Its funny but I have never seen a police officer near our office, although there are a number of foreigners working in the buildings alongside and some of them are also illegal.

We were actually discussing a posting on Legal Matters saying that the police and the law is going to focus on companies hiring illegal workers, like me and my friends.

Just as a security measure for us, I am wondering how you can get caught.
Do they need to catch you in the office??
Do they need to catch you working at your computer ???
If you are in the books as an employee, will they comb through the books to fond out this information ?
Will they just target big companies??
Usually I think when getting a visa it is easier to get a visa for a smaller company, as they are scrutinized less

Thanks
Mr. Hsin Tien

I think that the best security measure is for your employer to apply for the appropriate work permit, so that you and he are both acting in a fully responsible and fully legal manner.

I am sorry if this reply is overly blunt.