Palestine Press Agency has an article about the problem of counterfeit currency in Gaza.
The reporter posed as a currency exchanger and became friendly with a Gazan contact, as he asked for a quantity of shekels. The counterfeit money comes in all denominations, from 100 shekel notes down to fake 5 shekel coins!
A Palestinian Arab in el-Arish creates the fake money and transports them through Gaza tunnels. The reporter couldn't get the counterfeit shekels the first day because Hamas was watching, bit a few days later they smuggled them in through normal goods smuggled through the tunnels - in this case, in paint cans.
Gazan intermediaries keep in touch with the Egyptian side through SMS. Most of the people involved do not know each other so if they are caught the operation can remain intact.
The forged cash is then spent in Gaza City markets where the shop-owners get duped.