If you use Intrusion Detection System (IDS) technology, you should know that if the IDS machine is between the Internet and the VPN concentrator that decrypts the encrypted packets (e.g., on a demilitarized zone—DMZ—network), it won't be able to detect intrusion activity that occurs between VPN-connected machines. Most IDS sensors match packet payloads to a database of intrusion signatures so that they know when to flag something as suspicious. If the packets are encrypted, they'll look like gibberish to the IDS machine. If you want your IDS machine to be able to monitor network traffic from VPN connections, make sure you place the IDS machine behind the VPN concentrator so that the IDS machine checks the traffic after the VPN concentrator decrypts it. You can't use an IDS on a software VPN, which operates directly from one VPN host to another.
IPSec supports several different enciphering algorithms. The most commonly used algorithm, Advanced Encryption Standard (AES), is widely acknowledged as one of the strongest algorithms available for data encryption. With a minimum key length of 64 bits, AES is strong enough for almost any commercial application. Some vendors' IPSec implementations use the Data Encryption Standard (DES) or Triple DES (3DES) ciphers. DES, whose 40-bit key has been cracked, is generally considered a weak algorithm for all but the lowest security levels. 3DES fixes DES's problems by using the algorithm three times and providing an effective key length of 168 bits. Note that if your VPN solution supports only one algorithm, any devices you add in the future must use that algorithm as well.
HotSpot Shield is a product that has had some ups and downs in terms of our editorial coverage. Back in 2016, they picked up some very positive coverage based on founder David Gorodyansky comments about protecting user privacy. Then, in 2017, a privacy group accused the company of spying on user traffic, an accusation the company flatly denies. Finally, just this year, ZDNet uncovered a flaw in the company's software that exposed users. Fortunately, that was fixed immediately.