Method for selectively restricting access to computer systems

An apparatus for accepting access requests from a client computer connected to a server computer by a network, comprising:

• means for receiving an access request in the server computer from the client computer via the network;
• a random character generator generating a predetermined number of random characters to form a string in the server computer in response to the access request;
• means for modifying at least one perceptual attribute of the string of random characters to form a riddle configured to be easily answer by a human being with no advance knowledge of the riddle while being substantially difficult to answer by an automated agent unaided by a human being, the string being a correct answer to the riddle;
• means for rendering the riddle on an output device of the client computer, a correct answer to the riddle being the string;
• means for receiving an answer to the riddle from the client computer;
• means for determining if the answer to the riddle is correct;
• and
• means for accepting the access request if the answer is correct and received within a predetermined time interval and otherwise denying the access request, wherein the access request is denied when the access request is received from the automated agent.

A computer program product for use in conjunction with a computer system, the computer program product comprising a computer readable storage medium and a computer program mechanism embedded therein, the computer program mechanism for selectively accepting access requests from a client computer connected to a server computer by a network, the computer program mechanism comprising:

• instructions that receive an access request in the server computer from the client computer via the network;
• instructions that generate a predetermined number of random characters to form a string in the server computer in response to the access request;
• instructions that modify at least one perceptual attribute of the string of random characters to form a riddle configured to be easily answered by a human being with no advance knowledge of the riddle while being substantially difficult to answer by an automated agent unaided by a human being, the string being a correct answer to the riddle;
• instructions that render the riddle on an output device of the client computer;
• instructions that receive an answer to the riddle from the client computer;
• instructions that determine if the answer to the riddle is correct;
• instructions that accept the access request if the answer is correct and received within a predetermined time interval and that otherwise deny the access request, wherein the access request is denied when the access request is received from the automated agent.

A computer system for selectively accepting access requests from a client computer connected to a server computer by a network, comprising:

• a memory;
• and
• a processor to execute instructions stored in the memory, wherein the memory stores instructions that:
• receive an access request in the server computer from the client computer via the network;
• generate a predetermined number of random characters to form a string in the server computer in response to the access request;
• modify at least one perceptual attribute of the string of random characters to form a riddle configured to be easily answered by a human being with no advance knowledge of the riddle while being substantially difficult to answer by an automated agent unaided by a human being, the string being a correct answer to the riddle;
• render the riddle on an output device of the client computer;
• receive an answer to the riddle from the client computer;
• determine if the answer to the riddle is correct;
• and
• accept the access request if the answer is correct and received within a predetermined time interval and otherwise deny the access request, wherein the access request is denied when the access request is received from the automated agent.