Joomla have released an improtant update being version 1.6.3. This can be installed from within Joomla. However you may get a memory error message. this can be sorted by increasing the PHP memory limit on your Host server. We have adjusted this for all our clients. If you cannot access this function, then we can offer advice on alternatives. Or you can always upgrade the old fashioned method.
Also check the joomla website for important news on Joomla 1.7 being released in July.