Magento fatal error

Hi

We have a problem on our Magento site, we discovered that we had Malware on our server and our Hosting company Simple Servers have been asked to remove it this has led to the following, I have included their reply below -

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I just went ahead and remove the malicious codes from all your PHP files. However, your website started showing the following error, once this was done.
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Fatal error: Class 'Infortis_UltraMegamenu_Block_Navigation' not found in /home/bedrooma/public_html/app/code/core/Mage/Core/Model/Layout.php on line 491
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This is an urgent request if you feel you can have a look at the problem, please let me know and we can discuss the job further.

You can contact me on 07921 255219.

Regards
John Reynish