A firm's computer systems are flooded with thousands of seemingly legitimate requests, the sheer volume of which will slow or shut down the site's use. This might be caused by receiving spam from thousands of difficult$-$to$-$shut$-$down accounts. This is an example of

O a$.$ Data harvester

$$ b$.$ Malware Attacks

O c$.$ Stealing financial data

$$ O d$.$ Cash$-$out fraudster

O e$.$ DDoS attack