Cyber-spy groups, whose numbers are growing with little constraint, have begun hacking each other. Hellsing, a small and technically unremarkable cyber-espionage group, was subjected to a spear-phishing attack by another threat actor last year, before deciding to strike back with its own malware-infected emails.
The aftermath of the dust-up was uncovered by security researchers from Kaspersky Lab, who estimate further incidents along the same lines are likely.

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