Thank you for your answer. We have already contact our host. They answered that haven't changed anything. After May 28 one by one the TeX formulas from old courses that used TeX also disaperead. The host (on our request) restored the system from a backup. The old courses now work but the new written formulas work very selectively.
The PHP info (disable_functions row) reads like this:
Another problem persisits:
On the first page of our moodle site (http://www.regalia6.eu/moodle/) (this is, in index.php) appears a spam.
Thank you in advance