code: public static void setProperty(String key, String datum) {
          check("setProperty."+key);
          props.put(key, datum);
          increaseVersion();
          invalidateSMCache(key);  /* See below. */
      }
docs: Sets a security property value.
  
  <p>First, if there is a security manager, its
  <code>checkPermission</code> method is called with a
  <code>java.security.SecurityPermission("setProperty."+key)</code>
  permission to see if it's ok to set the specified
  security property value.
  
  @param key the name of the property to be set.
  
  @param datum the value of the property to be set.
  
  @throws  SecurityException
  if a security manager exists and its <code>{@link
  java.lang.SecurityManager#checkPermission}</code> method
  denies access to set the specified security property value
  @throws  NullPointerException if key or datum is null
  
  @see #getProperty
  @see java.security.SecurityPermission