Google employs many security measures to thwart would-be Google account hijackers, and not all are highly visible as the two-factor authentication option introduced in 2010 and 2011 (for corporate and non-paying customers, respectively).

Mike Hearn, Google Security Engineer, says that implementing all these measures has allowed Google to reduce the number of compromised accounts by 99.7 percent since 2011, when hijacking attempts were at their peak.

Still, the hijackers keep trying.

"We’ve seen a single attacker using stolen passwords to attempt to break into a million different Google accounts every single day, for weeks at a time. A different gang attempted sign-ins at a rate of more than 100 accounts per second," he shared in a blog post.

But every sign in attempt is evaluated before being approved. Google's system performs a complex risk analysis to determine how likely it is that the sign-in really comes from the account owner.

"In fact, there are more than 120 variables that can factor into how a decision is made," says Hearn. "If a sign-in is deemed suspicious or risky for some reason—maybe it’s coming from a country oceans away from your last sign-in—we ask some simple questions about your account."

Hijacking legitimate email accounts and using them to send malicious emails to the owners' contacts has become the preferred way for cyber criminals to target potential victims.

This trend is a testament to the effectiveness of modern-day spam filters, says Hearn, as they are good at blocking random spam, but occasionally let emails purportedly coming from an existent contact pass through.



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