An attacker can come up from behind and pull a purse from underneath a woman's arm very easily. Most women are concerned when they see someone in front of them and they clutch their purse tightly under their arm and grip it in the front with their hand. This does little to prevent an attacker from yanking the purse from under her arm from behind. The purse should be held in front of the body. This will cause an attacker to have to get closer to the woman and be in front to grab the purse.
A purse on a strap or in a shoulder bag gives many women a false sense of security. They tend to forget about the purse being there and are not as conscious of what is happening to it. The strap can be easily cut with snips or a razor with little or no feeling of the cutting being perceived by the woman. Suddenly she realizes the bag is gone. If she realizes this almost immediately, even then it will be too late. At most, all she will see is the backs of the attacker as he/she is running away. Again, if the purse is held in front of the body, there is less opportunity for the attacker, and the strap may make it more difficult for an attacker to grab the purse. Also, this causes the woman to be aware of the purse, instead of it just hanging at her side.
With a shoulder bag, the top should be clasped shut by the hand at all times. This prevents the contents from being lifted out. Even an amateur thief can lift a purse or wallet from the bag very easily without the woman knowing it occurred. When she does realize the purse is gone, many times she is not aware it was taken and may think she merely lost it. Keep the purse or wallet at the bottom of the bag. This may make it more difficult for you to get to the purse, but it also makes it difficult for the thief to get to it. This same advice also applies to a checkbook.