Squid Cache（简称为Squid）是一个流行的自由软件（GNU通用公共许可证）的代理服务器和Web缓存服务器。Squid有广泛的用途，从作为网页服务器的前置cache服务器缓存相关请求来提高Web服务器的速度，到为一组人共享网络资源而缓存万维网，域名系统和其他网络搜索，到通过过滤流量帮助网络安全，到局域网通过代理上网。Squid主要设计用于在Unix一类系统运行。Squid的发展历史相当悠久，功能也相当完善。除了HTTP外，对于FTP与HTTPS的支持也相当好，在3.0 测试版中也支持了IPv6。
Squid3.2的新特性包括
Squid 3.2 represents a new feature release above 3.1.
The most important of these new features are:
CVE-2009-0801 : NAT interception vulnerability to malicious clients.
NCSA helper DES algorithm password limits
SMP scalability
Helper Multiplexer and On-Demand
Helper Name Changes
Multi-Lingual manuals
Solaris 10 pthreads Support
Surrogate/1.0 protocol extensions to HTTP
Logging Infrastructure Updated
Client Bandwidth Limits
Better eCAP support
Cache Manager access changes
Squid 3.2.0.8 beta更新：
- Bug 3214: "helperHandleRead: unexpected read from ssl_crtd" errors.
- Bug 3043: Properly detect Iphlpapi.h on windows
- Bug 2055: Honor ICAP Max-Connections
- Fix NTLM/Negotiate reply auth PASSTHRU to peers
- Support SSL SNI to origin servers
- Add %EXT_LOG and %EXT_TAG external_acl_type format options
- Add %b tag for proxy listening port display in error pages
- Optimize base64 encoding/decoding
- Require libcap before enabling netfilter MARK support
- Require libtool 2.2
- Bundle pkg.m4 from pkg-config 0.25 for OS without pkg-config
- ... and all bug fixes and updates from 3.1.12.2
- ... and some documentation and code polishing

最新发布的 Squid 3.1.8修复了重大安全漏洞。
Changes to squid-3.1.5 (02 Jul 2010):
- Bug 2967: raw-IPv6 address URL with append_domain broken
- Bug 2950: HTTP responses with no Date, L-M or Expires can now be cached
- Bug 2943: ICAP tokens not logged when using multiple access
- Bug 2937: Fails to detect chunked encoding if not given in all lower case
- Bug 2903: does not send indirect X-Client-Ip in ICAP respmod
- Fix free memory corruption and off-by-one error when comparing SNMP OIDs
- Port from 2.7: max_filedescriptor config option
- Fix persistent_connection_after_error is meant to be on by default
- ... and several build errors.
squid-3.1.3 (3rd May 2010):
- Bug 2899: Regression: Restore lost rfc1738_unescape() data type
- Bug 2895: Regression: TPROXY2 compile errors
- Bug 2879: Regression: headers end-finding
- Bug 2874: Accept literal IPv6 address in icap_service URL
- Bug 2860: Regression: WCCPv1 handshake
- Bug 2848: Pass TCP_RST to client on early disconnect
- Fix tag ACL type not working
- squidclient: -k option to test connection keep-alive or close
squid-3.1.1 (29 Mar 2010):
- Bug 2873: undefined symbol
- Bug 2827: assertion in authentication
- Remove ufsdump binary from default builds
- Remove pinger from default startups
- ... and several documentation updates.
squid-3.1.0.17 (24 Feb 2010):
- Regression Fix: Non-English error page UTF encoding
- Bug 2616: reduce IdleConnList::removeFD messages
- Bug 1843: multicast-siblings cache_peer option
- Port from 2.7: X509 certificate alias-domain handling
- Add adapted_http_access option
- NTLMv2 support for fake NTLM helper
squid-3.1.0.16 (01 Feb 2010):
- Regression Fix: Make Squid abort on all config parse failures.
- Regression Bug 2811: SNMP client/peer table OID numbering
- Bug 2851: Connection pinning fails when using a peer
- Bug 2850: Mismatch in hier_code enum / hier_strings array
- Bug 2731: Add follow_x_forwarded_for support to ICAP
- Bug 2730: Regressions in follow_x_forwarded_for since Squid-2
- Bug 2706: Set timestamps during ICAP request satisfaction.
- Bug 2553: X-Forwarded-For with IPv6 address not handled correctly
- Fix: WCCPv1 not connecting to router correctly
- Remove obsolete RunCache/RunAccel scripts.
- Add client_ip_max_connections
- Add the http::>ha format code and make http::>h log original request headers
- ... and all bug fixes from 3.0 up to 3.0.STABLE22
- ... and many more minor build and display annoyances.
squid-3.1.0.15 (23 Nov 2009):
- Regression Fix: myip ACL not accepted in config
- Bug 2795: acl arp lookups including port
- Bug 2794: ESI parsing fails on FreeBSD
- Bug 2778: fix linking issues using SunCC
- Bug 2724: eCAP build failure unless ICAP enabled
- Bug 2628: Correct default PID location to PREFIX/var/run/squid.pid
- Bug 2617: Performance degradation during processing list of dstdomain ACL's
- Bug 2374: Support ICY / ICEcast / SHOUTcast streaming protocol.
- Fix: 64-bit filesize issue in squidclient POST of large files
- Fix: send correct Connection: header on intercepted replies
- Support libtool 2.x
- ESI libraries libexpat and libxml2 now optional
- ESI support default enabled
- Bump libcap minimum requirement to libcap 2.09+
- ARP / MAC support fixes for IPv6-mode
- Add outstanding IPv6 settings to squid.conf (localnet, localhost)
- ... and many additions to the background testing structure
- ... and very many minor build and code cleanups for non-GCC compilers.