Installation on more than one PC

I have purchased a license for CC Pro. I am a self-employed Technical Writer with 3 machines that I maintain. Am I required to buy separate licenses for each of these machines, or can I install CC Pro on each of these machines under the same license?I know that typically you are allowed only a single installation, but there is a caveat "with certain exceptions" stated on your website, but those exceptions are not explicitly stated or clarified.

Thank you.

The exceptions are stated in the next paragraph on that webpage:

https://support.piriform.com/hc/en-us/articles/204044464-How-many-computers-can-I-install-CCleaner-Professional-on-

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		We create licenses for our Professional and Business products (per computer) with some exceptions.<strong> For example, if you buy a boxed copy of CCleaner Professional in a retail store, you may be able to install it on more than one computer. Please check the box or packaging for more details.</strong>
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Boxed edtions for retail sale may, at various times, have included special offers (including possibly multi-machine offers) and some old stock may still be on the retailers shelves. Any offer on a boxed product will still be honoured.

Usually if you want a licence to cover 3 machines you would buy the 'Pro Plus' edition of CCleaner:

https://support.piriform.com/hc/en-us/articles/360028350711-How-many-computers-can-I-install-CCleaner-Professional-Plus-on-

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		The CCleaner Professional Plus bundle works on up to 3 computers
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For more than 3 machines you would want one of the Business editions:

https://www.ccleaner.com/business/ccleaner-product-matrix

If you have bought 'CCleaner Pro' but now want to upgrade it to 'CCleaner Pro Plus' to cover three machines then email support@ccleaner.com who should be able to help you.