Today's desktop computers can be sources of some electromagnetic radiation that can be dangerous.
The typical desktop computer has an internal switching power supply that works with the mains voltage, 120 or 230 V AC. Generally these power supplies are big sources of electromagnetic emissions on a wide frequency range. These emissions are almost completely shielded by the power supply metal box but there are still some emissions that travel away from the power supply along the power cord, and the other cables attached to the computer.
Some computer parts emit a lot of high frequency electromagnetic radiation. The amount of electromagnetic radiation emitted varies among the many brands and models of computer components. In general the emissions come from the computer processor, or CPU, the mainboard, the hard disks and the CD and DVD readers.
This electromagnetic radiation has a very high frequency so it is easily stopped by a metal wall, even a thin layer. Some kind of emissions are blocked also by non metal materials, like plastic.
Usually the computer components are all placed inside a metal box which is almost completely closed, and this is enough to prevent the electromagnetic radiation reaching the users. However in practice the enclosure can have large apertures, especially on the front side, so there can be spills of radiation, in particular directions.
Since this emissions may be concentrated in narrow beams they can remain unnoticed until somebody sits in a particular position respect to the computer box, and stays in the same position for some time.
These high frequency radiation is similar to that of cell phones and so it is dangerous. The symptoms of an exposure to this are various, like light pain and burning sensation of the skin, like the effect of very hot water, plus many other effects that may vary individually.
The high frequency emissions coming from the computer components can be stopped by means of some shield. If the front side of the computer box is not entirely metal then a possible solution is to apply a shield made of self-adhesive aluminum foil, possibly on the inside of the box. The shield can also be applied on the outside, just over the plastic cover. To avoid any damage to the plastic cover we suggest to cover the plastic with an adhesive paper tape like that used for painting cars, and then put the aluminum tape over the paper tape. The aluminum tape however must be in contact with the metal box, along a wide strip.
The low frequency emissions are almost impossible to shield and so the only solution, if this kind of emissions are too strong, is to put the computer box far enough from the users.
Finally, the effects of the switching power supply may be reduced by applying a good AC filter to the power cord right before it enters into the computer box.