No program should ever be allowed to modify the memory of a third-party program. This is exactly how trojan horses work: they attach themselves to a legit process like a web browser, and do their damage in the background.
This is not entirely true: There are legitimate reasons for why a program would modify the memory of another program: Debuggers, cheat programs, and even some forms of cracks and hiding software all have legitimate reasons for why they would modify the memory or executable space of a third-party program.
Most likely, however, in this case, the behavior is that of Evil Spywares.