Sharing and Unsharing Records in CRM 2011/2013

sharing

 // Create the request object and set the target and principal access

GrantAccessRequest grantRequest = new GrantAccessRequest()

            {

                Target = new EntityReference(Account.EntityLogicalName, accountId),

                PrincipalAccess = new PrincipalAccess()

                {

                    Principal = new EntityReference(SystemUser.EntityLogicalName, userId),

                    AccessMask = actionRights

                }

            };

 // Execute the request.

GrantAccessResponse granted = (GrantAccessResponse)service.Execute(grantRequest);

Unsharing 

 // Create the request object and set the target and revokee.

            RevokeAccessRequest revokeRequest = new RevokeAccessRequest()

            {

                Target = new EntityReference(Account.EntityLogicalName, accountId),

                Revokee = new EntityReference(SystemUser.EntityLogicalName, accountuserId)

            };

// Execute the request.

 RevokeAccessResponse revoked = (RevokeAccessResponse)service.Execute(revokeRequest);