Step 1: Recall the relevant provision.
Section 78 of the Information Technology Act, 2000 fixes the minimum rank of police officer allowed to investigate offences under the Act.
Step 2: Eliminate the wrong ranks.
A Sub-Inspector is too junior for this provision, while a Deputy Superintendent of Police and a Superintendent of Police are ranks above the actual minimum fixed after the 2008 amendment.
Step 3: Confirm the current minimum rank.
After the amendment, an officer not below the rank of Inspector is authorised to investigate offences under the IT Act.
\[ \boxed{\text{Inspector}} \]