The term tiger team was originally a military term for a team whose purpose is to penetrate security of "friendly" installations, and thus test their security measures. The members are professionals who install evidence of their success, e.g. leave cardboard signs saying "bomb" in critical defence installations, hand-lettered notes saying "Your codebooks have been stolen" (they usually haven't been) inside safes, etc. Sometimes, after a successful penetration, a high-ranking security person will show up later for a "security review," and "find" the evidence. Serious successes of tiger teams sometimes lead to early retirement for base commanders and security officers.

The term has become popular in the computer world, where the security of computer systems is often tested by tiger teams; one of the earliest examples was with the Multics operating system. A subset of tiger teams are professional crackers, testing the security of military computer installations by attempting remote attacks via networks or supposedly "secure" communication channels. Some of their escapades, if declassified, would probably rank among the greatest hacks of all time.

The term is now obsolete, and it is now more common to refer to penetration testers or security testers and the process of assessment of a computer system or network infrastructure as penetration testing.

Recently, and more generally, it has come to mean any official inspection team or special "firefighting" group called in to look at a problem.