  We study the viscosity driven (Jacobi-like) bar mode instability of rapidly
rotating strange stars in general relativity. A triaxial, "bar shaped" compact
star could be an efficient source of continuous wave gravitational radiation in
the frequency range of the forthcoming interferometric detectors. We locate the
secular instability point along several constant baryon mass sequences of
uniformly rotating strange stars described by the MIT bag model. Contrary to
neutron stars, strange stars with T/|W| (the ratio of the rotational kinetic
energy to the absolute value of the gravitational potential energy) much lower
than the corresponding value for the mass-shed limit can be secularly unstable
to bar mode formation if shear viscosity is high enough to damp out any
deviation from uniform rotation. The instability develops for a broad range of
gravitational masses and rotational frequencies of strange quark stars. It
imposes strong constraints on the lower limit of the frequency at the innermost
stable circular orbit around rapidly rotating strange stars. The above results
are robust for all linear self-bound equations of state assuming the growth
time of the instability is faster than the damping timescale. We discuss
astrophysical scenarios where triaxial instabilities (r-mode and viscosity
driven instability) could be relevant in strange stars described by the
standard MIT bag model of normal quark matter. Taking into account actual
values of viscosities in strange quark matter and neglecting the magnetic field
we show that Jacobi-like instability cannot develop in any astrophysicaly
interesting temperature windows. The main result is that strange quark stars
described by the MIT bag model can be accelerated to very high frequency in Low
Mass X-ray binaries if the strange quark mass is ~ 200 MeV or higher.
