The Jargon File (version 4.4.7, 29 Dec 2003):

tiger team
 n.

    [U.S. military jargon]

    1. Originally, a team (of sneakers) whose purpose is to penetrate
    security, and thus test security measures. These people are paid
    professionals who do hacker-type tricks, e.g., leave cardboard signs saying
    ?bomb? in critical defense installations, hand-lettered notes saying ?Your
    codebooks have been stolen? (they usually haven't been) inside safes, etc.
    After a successful penetration, some high-ranking security type shows up
    the next morning for a ?security review? and finds the sign, note, etc.,
    and all hell breaks loose. Serious successes of tiger teams sometimes lead
    to early retirement for base commanders and security officers (see the 
    patch entry for an example).

    2. Recently, and more generally, any official inspection team or special 
    firefighting group called in to look at a problem.

    A subset of tiger teams are professional crackers, testing the security
    of military computer installations by attempting remote attacks via
    networks or supposedly ?secure? comm channels. Some of their escapades, if
    declassified, would probably rank among the greatest hacks of all times.
    The term has been adopted in commercial computer-security circles in this
    more specific sense.


The Free On-line Dictionary of Computing (30 December 2018):

tiger team

   (US military jargon) 1. Originally, a team whose purpose is to
   penetrate security, and thus test security measures.  These
   people are paid professionals who do hacker-type tricks,
   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.
   After a successful penetration, some high-ranking security
   type shows up the next morning for a "security review" and
   finds the sign, note, etc. and all hell breaks loose.  Serious
   successes of tiger teams sometimes lead to early retirement
   for base commanders and security officers (see the patch
   entry for an example).

   2. Recently, and more generally, any official inspection team
   or special firefighting group called in to look at a
   problem.

   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 times.  The term has been adopted in commercial
   computer-security circles in this more specific sense.

   [Jargon File]