Jacob Hoffman-Andrews writes:
Recently, Verizon was caught tampering with its customer’s web requests to inject a tracking super-cookie. Another network-tampering threat to user safety has come to light from other providers: email encryption downgrade attacks. In recent months, researchers have reported ISPs in the US and Thailand intercepting their customers’ data to strip a security flag—called STARTTLS—from email traffic. The STARTTLS flag is an essential security and privacy protection used by an email server to request encryption when talking to another server or client.1
Read more on EFF.