Virus in foreign street linked to a certain block (6-5)

'virus in foreign' is the definition.
I know nothing about this answer so I cannot judge whether this works.

'street linked to a certain block' is the wordplay.
I cannot quite see how this works, but
'street' could be 'st' (abbreviation) and 'st' is located in the answer.
'a' could be 'one' and 'one' is present in the answer.
The remaining letters 'sarsen' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

Can you help me to learn more?