A phone scam is thought to have been attempted on people in Worthing and Lancing at least eight times today.
Now police are warning residents, particularly elderly and vulnerable people, not to be fooled.
The fraudsters pretend to be bank or police officials to try to obtain confidential details of their accounts.
They try to persuade victims to withdraw money from their banks and hand it to a pre-arranged courier to be securely processed.
In fact, it simply disappears into the hands of the criminals.
As part of the scam, fraudsters may invite their victim to ring their bank or the police to convince them that the call is genuine.
But by keeping the line open at their end, the criminals are able to take these calls themselves and use accomplices to play the part of officials.
Police say it is important not to ring immediately but to leave at least ten minutes before using the same phone or else use an alternative phone, such as a mobile, to call bank or police.
A police spokesman said: "If you doubt the credentials or intentions of anybody calling you, or you receive a suspicious telephone call asking for bank details or instructing you to withdraw money or purchase a money voucher, we urge you to contact police immediately.
"No genuine organisation will ever ask to collect money or bank cards from your home or ask you to confirm a PIN [personal identification number].
"If you receive a suspicious telephone call of this nature, call 101 or email email@example.com quoting Operation Edisto.
"If somebody is at your door, or if you believe somebody is on their way to your address expecting to collect money or bank details from you, call police on 999 immediately."