In computer security, the term specially malformed
is used to describe poisoned input. In theory, it means any input that was deliberately created to exceed the expectations of a normal, naive user.
In practice, it usually means that the programmer failed to account for all possible input, and someone has come up with a buffer overflow attack or something similar.
The most common specially malformed input is a long string of capital A's -- often thousands in a row. AAAAAAAAAAA... is used mostly because it leaves an obvious trail in hex; you can examine the results of your attack by looking for the repeating hex code 414141414141...
So, for example, you could use a Web browser to request the URL http://www.targetsite.int/AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA... and see if it crashes or something.