Infantry
The tank is still vulnerable to infantry, especially in close country or built up areas. The armour and mobility of tanks, while usually notable assets, also makes them large and noisy. This can give enemy infantry the initiative, allowing them to spot, track and evade tanks until an opportunity presents itself for a stealthy counter-attack. This is why modern tactics insist on tanks being closely supported by friendly infantry.
For veteran troops, it is relatively easy for an infantry man to get close to a tank, especially if it is fully closed down (that is, the commander is fully inside the turret) as tanks have very poor visibility close in and especially to the sides and rear, unless the turret is pointing in that direction. If the crew commander is not closed down, that is, has exposed his head and perhaps upper body for the better view it affords him, then he can of course be shot.
Once an infantry man is close to a tank he cannot be targeted by its main weaponry unless the crew expose themselves to attack him, as the main gun and coaxial machine gun can not depress sufficiently to engage the close-in infantry man. Where tanks are operating in groups this is less of a problem, since they can call on nearby tanks to fire on themselves with machine guns and other light weapons which are unlikely to damage a tank but which will drive off infantry.
Whilst many handheld infantry antitank rockets, missiles and grenades will not penetrate the front armour of a tank, they will, generally speaking, penetrate the weaker, rear, top and perhaps sides, as well as being able to easily damage the running gear to inflict an "M" (mobility) kill. Tanks are also vulnerable to hand placed antitank mines.
In addition in built up areas the tank is very vulnerable to attack from above—the roof and floor of the tank being traditionally the thinnest and weakest armoured surfaces.
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Mines
The tank is still vulnerable to mines. Mines have the advantage of attacking the thinnest armour of the tank and can be well concealed.
In addition with modern scatterable mines, and in particular artillery scatterable mines, it is actually possible to lay a mine field around a moving tank formation.
As well as the traditional bottom attack mine, the scatter mine, the artillery delivered mine, or air delivered mine, there are also a number of side attack or "off route" mines available. These are mines that can be mounted on a vertical surface such as a wall, or tree, or mounted on a stand and are intended to be aimed at a road, track to other point a tank is likely to pass. Choke points such as bridges, fords, gates, underpasses, etc. are all likely spots. When the tank passes they fire into the side of the tank. The two common warheads for these mines are the ubiquitous HEAT and less commonly a platter charge. These mines can be fired by a human operator, simple mechanical actuator such as a tripwire or pressure plate, or by more sophisticated systems, such as seismic, IR or other electronic fusing systems. Some of the fusing systems are sophisticated enough to be able to discriminate between different classes of target and only attack specified classes of vehicles, e.g., ignore wheeled vehicles. Obviously a well placed off route mine will attempt to attack the rear or at worst the side of the tank, if at all possible. Some infantry antitank weapons can also be configured to act as off-route mines.
http://en.wikipedia.org/wiki/Tanks