Can a previously invented technology infringe a recent patent?

You have not really provided enough facts to truly determine the correct situation. For example, when you say that you kept the technology confidential, was it still in public use but could not readily be determined/detected. The classic Coca-Cola situation comes to mind - allegedly, for years, the precise composition of Coke was a trade secret, yet Coke was being publicly sold - therefore, Coca-Cola themselves could not get a patent because the composition had been in public use for years, and no one else could get a patent for the composition for the same reason - according to 35 USC 102(a), a person is entitled to a patent unless the subject matter was in use or on sale prior to the effective filing date of the patent application. So, in Coca-Cola's case, no one can get a patent. So, if your situation is the same - the technology is still, in effect, confidential, but it has been in public use for two years, then no one can get a patent on it, and you will not infringe the patent if they obtain the patent, or if they obtain the patent and allege infringement against you, you can effectively invalidate their patent based upon public use prior to their filing for their patent. On the other hand, if you did not publicly use the technology, then this other party could in fact obtain a patent and then you would likely infringe their patent.