Old server's corrupted — firm employed draws lines through (10)

'employed draws lines through' is the definition.
I know nothing about this answer so I cannot judge whether this works.

'old server's corrupted firm' is the wordplay.
I cannot quite see how this works, but
'old' could be 'o' (common abbreviation eg in OE for Old English) and 'o' is found in the answer.
'firm' could be 'co' (abbreviation for company) and 'co' is found in the answer.
an anagram of 'server' is 'versre' which is within the left over letters.
A single letter 's' remains which might be clued in a way I don't see.
This explanation may well be incorrect...

Can you help me to learn more?