Identifying polymorphic malware

1. A method of identifying an electronic file as polymorphic malware, the method comprising:

at a server, receiving from a client device a hash value and metadata associated with an electronic file;

comparing the metadata with corresponding metadata stored at a database;

determining that the received metadata relates to corresponding metadata stored at a database, the corresponding stored metadata being associated with a further hash value that differs from the received hash value;

determining that the received hash values have been reported by fewer than a predetermined number of clients; and

as a result, determining a likelihood that the electronic file is polymorphic malware and prioritizing the electronic file for further analysis.

2. The method according to claim 1 , further comprising;

comparing the received hash value and metadata with known fingerprints stored at the database;

in the event that any of the received hash value and/or metadata corresponds to at least a portion of a fingerprint stored at the database, determining that the electronic file is clean or malware.

3. The method according to claim 1 , further comprising, in the event that a determination of the likelihood that the electronic file is polymorphic malware cannot be made, alerting a user.

4. The method according to claim 1 , further comprising adding the received metadata to the database.

5. The method according to claim 1 , further comprising at the server, generating a fingerprint for the electronic file, the fingerprint being based on the received metadata.

6. An anti-virus server comprising:

a receiver for receiving from a client device a received hash value and received metadata associated with an electronic file;

means to access a database in which are stored records of queries from other client devices, each record comprising a hash value and metadata, the metadata being stored in clusters of metadata;

a processor for comparing the metadata with corresponding metadata stored at the database; and

further arranged for determining that the received metadata is similar to corresponding metadata stored at the database, the corresponding stored metadata being associated with a further hash value that differs from the received hash value;

the processor being further arranged to determine that fewer than a predetermined number of queries including hash values matching the received hash value have been received by the server; and

the processor is further arranged to prioritize the electronic file for further analysis in the event that a determined likelihood indicates that the electronic file is polymorphic malware.

7. The anti-virus server according to claim 6 , wherein the processor is arranged to compare the received hash value and metadata with known fingerprints stored at the database and, in the event that any of the received hash value and metadata corresponds to at least a portion of a fingerprint stored at the database, determine that the electronic file is clean or malware.

8. The anti-virus server according to claim 6 , wherein the processor is further arranged to alert a user in the event that a determination of the likelihood that the electronic file is polymorphic malware cannot be made.

9. The anti-virus server according to claim 6 , wherein the processor is further arranged to add the received metadata to the metadata cluster.

10. The anti-virus server according to claim 6 , wherein the processor is arranged to generate a signature for the electronic file, the signature being based on the received metadata.

11. A non-transitory program storage device comprising computer readable code which, when run on a server, causes the server to perform the method as claimed in claim 1 .